His Piousness and Contentment:

Imam Hasan had the worldly possessions at his disposal and could have well enjoyed a luxurious life, but he utilized all of it in the betterment of the condition of the poor. He was so courteous and humble that he never hesitated to sit along with the beggars in the lanes and on the thoroughfares of Medina to reply to some of their religious queries. Through his cordial attitude and hospitality he never let the poor and the humble feel inferior to him when they visited his abode.

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Imamate:

The demise of the Holy Prophet was followed by an eventful era when the Islamic world (under the false ruling bodies) came in the grip of the fever of expansionism and conquest. But even under such a revolutionary phase, Imam Hasan kept devoting himself to the sacred mission of peacefully propagating Islam and the teachings of the Holy Prophet along with his great father Imam 'Ali. The martyrdom of Imam 'All on the 21st Ramadan marked the inception of Imam Hasan's Imamate. The majority of Muslims pledged their allegiance to him and finalized the formality of bay'ah (oath of allegiance). No sooner had he taken the reins of leadership into his hands than he had to meet the challenge of Mu'awiyah, the Governor of Syria, who declared a war against him. In compliance with the Will of Allah and with a view to refrain from causing the massacre of Muslims however, he entered into a piece treaty with Mu'awiyah on terms (though not totally respected and carried out by Mu'awiyah), yet saved Islam and stopped a civil war. But this peace treaty was never meant as a surrender by him of the permanent leadership to Mu'awiyah. It was meant only as an interim transfer of the administration of the Islamic kingdom, subject to the condition that the ad- ministration would be surrendered back to Imam Hasan after Mu'awiyah's death and then it would in turn be inherited by Imam Husayn. Having relieved himself of the administrative responsibilities, Imam Hasan kept the religious leadership with himself and devoted his life to the propagation of Islam and the teachings of the Holy Prophet in Medina.

Martyrdom:

Mu'awiyah's malice against Imam Hasan led him to conspire with the Imam's wife Ja'dah, the daughter of Ash'ath. She was made to give the Imam some poison which affected his liver. Imam Hasan thus succumbed to Mu'awiyah's fatal mischief and attained his martyrdom on 28th Safar 50 AH. His funeral was attended by Imam Husayn and the members of the Hashimite family. His bier while being taken for burial to the Holy Prophet's tomb was shot at with arrows by his enemies, (under direct supervision and consent of 'A'ishah), and it had to be diverted for burial to the Jannatu 'I-Baq;' at Medina. His tomb was demolished along with others on 8th Shawwal 1344 (21st April 1926) by the Saudi rulers when they came to power in .Hijaz. The terms of the peace treaty were soon violated, but earned only a short-lived glory for Mu'awiyah. Its aftermath proved disastrous and doomed the fate of his son Yzid and dealt a fatal blow to the entire family of Umayyads. After the death of Mu'awiyah, Imam Husayn emerged as the insurmountable mountain of truth and determination. In the gruesome tragedy of Karbala', by sheer force of numbers, and by isolating the seventy-two members of Imam Husayn' s party and stopping them from even getting water to drink for three days, Yazid succeeded in annihilating the seventy-two persons including members of the Imam's family who were with him. This dastardly success of Yazid was, however, short-lived. The Muslims turned against him on learning of the heinous act he had committed and this resulted in the downfall of Yazid and the extinction of the Umayyad power from the face of the earth.

Allamah Tabatabai writes:

Imam Hasan Mujtaba, upon whom be peace, was the second Imam. He and his brother Imam Husayn were the two sons of Amir al-Mu'minin 'Ali and Hadrat Fatimah, the daughter of the Prophet. Many times the Prophet had said, "Hasan and Husayn are my children." Because of these same words 'Ali would say to his other children, "You are my children and Hasan and Husayn are the children of the Prophet." Imam Hasan was born in the year 3 AH, in Medina and shared in the life of the Prophet for somewhat over seven years, growing up during that time under his loving care. After the death of the Prophet which was no more than three, or according to some, six months earlier than the death of Hadrat Fatimah, Hasan was placed directly under the care of his noble father. After the death of his father, through Divine Command and according to the will of his father, Imam Hasan became Imam; he also occupied the outward function of caliph for about six months, during which time he administered the affairs of the Muslims.

During that time Mu'awiyah, who was a bitter enemy of 'Ali and his family and had fought for years with the ambition of capturing the caliphate, first on the pretext of avenging the death of the third caliph and finally with an open claim to the caliphate, marched his army to Iraq, the seat of Imam Hasan's caliphate. War ensued during which Mu'awiyah gradually subverted the generals and commanders of Imam Hasan' s army with large sums of money and deceiving promises until the army rebelled against Imam Hasan. Finally, the Imam was forced to make peace and to yield the caliphate to Mu'awiyah, provided it would again return to Imam Hasan after Mu'awiyah's death and the Imam's Household and partisans would be protected in every way. In this way Mu'awiyah captured the Islamic caliphate and entered Iraq. In a public speech he officially made null and void all the peace conditions and in every way possible placed the severest pressure upon the members of the Household of the Prophet and the Shi'ah.

During all the ten years of his Imamate, Imam Hasan lived in conditions of extreme hardship and under persecution, with no security even in his own house. In the year 50 AH, he was poisoned and martyred by one of his own House- hold who, as has been accounted by historians, had been motivated by Mu'awiyah. In human perfection Imam Hasan was reminiscent of his father and a perfect example of his noble grand- father. In fact, as long as the Prophet was alive, he and his brother were always in the company of the Prophet who even sometimes would carry them on his shoulders. Both Sunni and Shl'ite sources have transmitted this saying of the Holy Prophet concerning Hasan and Husayn: "These two children of mine are Imams (leaders) whether they stand up or sit down" ( allusion to whether they occupy the external function of caliphate or not). Also, there are many traditions of the Holy Prophet and 'Al concerning the fact that Imam Hasan would gain the function of Imamate after his noble father. (Shi'ite Islam).

Imam al-Hasan ibn 'Ali', peace be on him, said:

If you fail to obtain something of worldly benefit, take it as if the thought of it had never crossed your mind at all.

Never did a nation resort to mutual counsel except that they were guided by it towards maturity.

It is love which brings closer those who are remote by ancestry, and it is (the absence of) love which causes dissociation between those who are related by ancestry.

Opportunity is something which is quick to vanish and late to return.

source : http://www.hadith.net