This alliance was of great importance that on the one hand, it was the origin of the progeny of the Prophet (a.s) and on the other, the enemies of Islam were quietened who were blaming him of being issueless. Although the Prophet (a.s) male issues did not survive, Hasan (a.s) and Husayn (a.s) on account of being the sons of his daughter, Fatimah al-Zahra’, were accepted as his sons and through them his progeny prospered and spread throughout the world. Therefore, the Prophet (a.s) said:
“Allah has put the progeny of all other prophets in their backbones and my progeny in the backbone of `Ali ibn Abi-Talib (a.s)”
Whether the offspring is from the daughter or from the son, it is certainly the offspring of the parents! Not considering the children of daughters as the offspring of the father was the practice of the Days of Ignorance. In those days, some persons considered it a shame to give a daughter in marriage to another family. They used to think that they were sending the daughter as a slave to the other house. In some tribes, they considered a great honor to bury the newborn daughters alive. When these daughters somehow survived and were married, their children were looked down upon as outcasts. Therefore, an Arab poet of those days has very nicely described this tendency:
Our sons’ sons are our sons. Our daughters’ sons are but strangers!
The Prophet of Islam (a.s) termed the daughters’ offspring as the fathers’ offspring and abolished the practice of the Days of Ignorance that only the sons’ offspring deserve to be accepted as the offspring of a family. Therefore, whenever he mentioned about the sons of Fatimah al-Zahra’, he called them his own sons. Imam al-Hasan and Imam al-Husayn (a.s) too addressed him as father. They addressed `Ali (a.s) as Abul-Hasan. But after the expiry of the Prophet (a.s), Imam al-Hasan and Imam al-Husayn (a.s) started calling `Ali
 Al-Sawā`iq al-Muhriqah, Page 154
(a.s) as father. `Ali (a.s) too considered them as the sons of the Prophet (a.s) on account of being Fatimah al-Zahra'’s sons. Therefore, at the Battle of Siffin, when Imam al-Hasan (a.s) went forward to combat, `Ali (a.s) said,
“Stop this youth from going to combat! His death will make me weak and shattered because I am shy of putting these two youths (Hasan and Husayn) in the mouth of death lest the progeny of the Prophet (a.s) is extinguished!”
Once, Abul-Jarūd told Imam al-Baqir (a.s) that when the verse of Mubahalah, “…our sons and your sons” was presented as proof of Imam al-Hasan and Imam al-Husayn (a.s) being the sons of the Prophet (a.s), some people said, “Of course, the daughters’ children are the progeny but are not born from the backbone of the father!” The Imam (a.s) said that Allah says in the Holy Qur’an about taboo women:
And the wives of your sons born from your backbone are taboo (haram) for you (to marry).
The Imam (a.s) told Abul-Jarūd to ask the objectors whether it was permissible for the Prophet (a.s) to marry the spouses of Imam al-Hasan and Imam al-Husayn (a.s). If they said in the affirmative, they will be wrong. If they say that he cannot marry them, the only reason for it being taboo is that they were the wives of the Prophet’s born of his backbone (sulb).
Ibn Babawayh al-Qummi has written that when Imam Mūsa al-Kazim (a.s) was called to the court of Harūn al-Rashid, the ruler asked him why he was called the progeny of the Prophet (a.s) although you are the progeny of `Ali (a.s) and the lineage descends from the father. The Imam (a.s) said, “If the Prophet (a.s) came back to the world and claims matrimonial relationship with you, will you accept it?” Harūn replied, “Most willingly! This relationship for us is the matter of great pride!” Hearing this, the Imam (a.s) said:
“But he cannot claim to establish matrimonial relationship with us and nor can we give him our relationship because we are his progeny and you are not!”
Muhammad ibn Talhah al-Shafi`i writes in Matalib al-Sa’ūl that al-Hajjaj ibn Yūsuf al-Thaqafi that whenever al-Shi`bi mentioned the names of Imam al-Hasan and Imam al-Husayn (a.s) he mentioned about them as the sons of the Prophet (a.s). Al-Hajjaj got furious over it and called him to reprimand. When
 Nahj al-Balāghah
 `Uyūn al-Akhbār
al-Shi`bi reached the court, he found a group of scholars of al-Kūfah sitting there. Al-Hajjaj asked him, “I have heard that you call Hasan and Husayn the sons of the Prophet although they were not his sons but the sons of his daughter Fatimah, and the progeny is not identified through the mothers!” Al-Shi`bi remained quiet for some moments and then recited the following verse from the Holy Qur’an:
وَوَهَبْنَا لَهُ إِسْحَاقَ وَيَعْقُوبَ كُلاًّ هَدَيْنَا وَنُوحًا هَدَيْنَا مِنْ قَبْلُ وَمِنْ ذُرِّيَّتِهِ دَاوُودَ وَسُلَيْمَانَ وَأَيُّوبَ وَيُوسُفَ وَمُوسَى وَهَارُونَ وَكَذَلِكَ نَجْزِي الْمُحْسِنِينَ وَزَكَرِيَّا وَيَحْيَى وَعِيسَى وَإِلْيَاسَ كُلٌّ مِنْ الصَّالِحِينَ
“And form the progeny of Ibrahim, Dawūd, Sulayman, Ayyūb, Yūsuf, Mūsa, and Harūn were the guided ones; thus, We reward the righteous. And Zakariyya, Yahya, `Isa and Ilyas were Guided. They were all of Allah’s virtuous creatures. (6:84-85)”
After reciting this verse, al-Shi`bi said that `Isa -Jesus- (a.s) too has been included in the Progeny of Ibrahim (a.s) definitely because he descended Ibrahim (a.s) through his mother Maryam. When we treat `Isa (a.s) as the progeny of Ibrahim (a.s) through his mother Maryam bint `Imran, then why Imam al-Hasan and Imam al-Husayn (a.s) cannot be termed the progeny of Muhammad (a.s) through his daughter Fatimah al-Zahra’, their mother! In the case of `Isa (a.s) there was a difference of several generations between his ancestor, Ibrahim (a.s) and himself. But in the case of Imam al-Hasan and Imam al-Husayn (a.s), they were the next of kin to the Prophet (a.s)! Hearing this al-Hajjaj kept quiet.
Once `Amr ibn al-`As criticized `Ali (a.s) for calling Imam al-Hasan and Imam al-Husayn (a.s) as the sons of the Prophet (a.s). When the Imam (a.s) heard this he asked the informer to tell the enemy of Allah (`Amr) that if they are not his sons, then the Prophet (a.s) would be termed abtar (issueless) as his father al-`As ibn Wa’il used to call the Prophet (a.s). The truth is that Allah has termed the enemies of the Prophet (a.s) abtar instead of him!
Mu`awiyah’s slave Dhakwan says that once Mu`awiyah said that instead of calling Hasan and Husayn (a.s) as the sons of the Prophet (a.s) they should be called the sons of `Ali (a.s) because they are not from the backbone of the Prophet (a.s).
Dhakwan says further that Mu`awiyah instructed him to prepare a list of his progeny. He prepared a roster of his sons and the grand children and presented to his master. Mu`awiyah asked him why he did not add the names of his grand children through his daughters. Dhakwan said how they could
come in the roster of your progeny when they are the children of your daughters. Mu`awiyah understood his point and said that every word is said according to the situation!
It is surprising that Mu`awiyah accepted even the illegitimate son of his father, Ziyad ibn Sumayyah, as the son of Abū-Sufyan against the norms of Islam. But those whom Allah and His Prophet (a.s) themselves recognized as the sons of the Prophet (a.s) he blatantly refused to accept them as such.
About Abū-Jahl’s Daughter
`Ali (a.s) neither married a second wife during the lifetime of Fatimah al-Zahra’ (a.s) nor he ever thought of another marriage while she was alive. But some inimical narrators have concocted stories to malign him. The story is that `Ali (a.s) wanted to marry Abū-Jahl’s daughter by name Juwayriyyah or Jamilah. When the Prophet (a.s) heard about this, he was very upset and opposed the idea. Therefore, Musawwir ibn Makhramah says that `Ali (a.s) wished to marry the daughter of Abū-Jahl and when Fatimah heard about it, she complained to the Prophet (a.s) and said that the people of his clan have started saying that he had not the slightest care for his daughters and that `Ali (a.s) was bringing another woman home in the person of Abū-Jahl’s daughter! When the Prophet (a.s) heard this, he was very upset, went to the pulpit and said:
“I do not make the legitimate (halal) as illegitimate (haram) and legitimate as illegitimate, but By Allah! The Prophet’s daughter and the daughter of Allah’s enemy cannot be united in matrimony with one person!”
Another narration in this connection is that Musawwir ibn Makhramah heard the Prophet (a.s) say from the pulpit that Banū-Husham ibn Mughirah had sought his permission to give their daughter in marriage to `Ali (a.s). He replied:
“I do not permit! I do not permit! I do not permit! But if the son of Abū-Talib gives divorce to my daughter, he can enter into matrimony with that girl!”
This and many such narratives are attributed to Musawwir ibn Makhramah. This person was the nephew of `Abd al-Rahman ibn `Awf and was born two
 Tārīkh al-Khamīs, Vol 1, Page 412
 Tārīkh al-Khamīs , Vol 1, Page 412
years after the Migration in Makkah and moved to al-Madinah in 8 A.H. Ibn Hajar al-`Asqalani writes about him:
“Two years after the Hegira he was born in Makkah. He came to al-Madinah at the end of Dhul-Hijjah, 8 A.H.”
The author of al-Isabah writes:
“He was born two years after the Hegira and after the conquest of Makkah, Dhul-Hijjah 8 A.H. he came to al-Madinah when his age was six years.”
Makkah was captured in 8 A. H. and the concocted story too was dated around the same period. Until that time Abū-Jahl’s children had not embraced Islam. Therefore, on the day of the capture of Makkah, Bilal had sounded the adhan standing near the Ka`bah, the same Juwayriyyah bint Abū-Jahl demonstrated her infidelity when she said:
“God has kept my father safe from hearing the crude voice of Bilal!”
There is no question of matrimony with an infidel like this. The surprising thing is that the old companions are quiet and a child of six years becomes a narrator! And the bigger surprise is that the erudite scholars who reject the evidence of Ibn `Abbas regarding the event of Qirtas saying that the small child cannot be trusted to report correctly, accept and quote the story concocted by Musawwir ibn Makhramah. If there were ant truth in these stories, the governor of Syria would be the first to make all possible use of them. Even Umm al-Mu’minin `A’ishah would be too pleased to talk about these things. But the silence of these two persons proves beyond doubts that they too believed that the stories are concocted.
Also considering `Ali’s nature one cannot imagine his doing anything without consulting and seeking the permission of the Prophet (a.s) or to think of doing anything that might have hurt or disturbed him. There are several points to ponder while rejecting these stories outright:
How can we imagine that `Ali (a.s) could quietly plan matrimony with Abū-Jahl’s daughter and she seeks the permission of the Prophet (a.s) for such an alliance. Is such a thing possible from a person who never took a step without the consent of the Prophet (a.s)!
 Tahdhīb al-Tahdhīb, Vol 10, Page 151
 Al-Isābah, Vol 3, Page 399
 Tārīkh Abul-Fidā, Page 145
How is it possible that the Prophet (a.s) would term legitimate as illegitimate in ire, even if it is for his personal consideration. While the Prophet (a.s) is known for his strict observance of the norms of Shari`ah, how can one imagine his anger even if his daughter was faced with the prospect of the second woman to share her home and hearth! We can therefore conclude that the narrations quoted are sheer concocted stories.
Here it is of interest to quote an incident about al-Ma’mūn, the `Abbasid ruler. Al-Ma’mūn gave his daughter Umm al-Fadl in marriage to Imam Muhammad al-Taqi (a.s).The Imam (a.s) took her along to al-Madinah. From al-Madinah she wrote to her father that Imam Muhammad al-Taqi (a.s) had some slave girls at his home. Al-Ma’mūn wrote to her angrily:
“We have not married you to him to make whatever is legitimate for him illegitimate. Do not ever repeat such complaints again!”
When a worldly ruler like al-Ma’mūn was so particular about things termed legitimate by the Shari`ah, even though the interest of his own daughter was involved, then how could one imagine that the Prophet (a.s) would wave aside the norms of Shari`ah to side with his daughter. Can we imagine the Prophet (a.s) going to the pulpit to air his ire? Can we imagine `Ali (a.s) defying the Prophet (a.s) if he asked him to desist from doing certain things? The story does not hold water when it says that the Prophet (a.s) angrily said that the daughter of the Prophet (a.s) and an infidel enemy of Allah’s daughter could not be under one roof. When it is well-known that Ummu-Habibah bint Abū-Sufyan, Safiyyah bint Huyay, his own spouses, were the daughters of known infidels and the enemies of Allah!
The truth behind all this concoction is that when the enemies of `Ali (a.s) did not get anything against him, they went around spinning such yarn and canard. The cunning adopted by them is that they want to show the nobility of Fatimah and her importance in the eyes of the Prophet (a.s), but their main aim is to belittle `Ali (a.s) in the consideration of the common Muslims by spreading such stories.
 Al-Sawā`iq al-Muhriqah, Page 123
source : http://www.maaref-foundation.com/