No summons to Islam had yet been made in public, but there was an ever-increasing group of devout believers and intense worshippers, both men and women, most of them young.
After the revelation of the verse
"Warn thy family, who are thy nearest of kin."
The Holy Prophet(pbuh&hf) immeadiately called his little cousin Ali to him, and said,
"God hath commanded me to warn my family, of my nearest of kin, and the task is beyond my strength. But make ready food, with a leg of mutton, and fill a cup with milk, and assemble together the Bani Abd Al-Muttalib, that I may tell them that which I have been commanded to say."
Ali did exactly as he had been told, neither more nor less, and most of the clan of Hashim came to the meal, about forty men, in all had assembled.
Ali said
"When they were assembled, The Prophet told me to bring in the food which I had prepared. Then he took a piece of the meat, and bit a piece of it, and then cast the rest of it back again into the main dish, saying:
'Take it in the Name of God'
The men ate in relays, several at a time, until not one of them could eat any more. But behold, I could see no change in the food, except that it had been stirred by men's hands, and by my life, if they had been but only one man, he could have eaten all that I had put before them. Then The Holy Prophet said:
'Give them to drink Ali.'
So I brought the cup, and each of the men seated drank his fill. Though one man alone could have emptied that cup. But when The Holy Prophet was about to address them,
When Abu Lahab interupted and forestalled The Holy Prophet, and said,
'Come! Your host hath placed a spell upon you!'
Where upon at they all dispersed before he could even speak."
The Next Day
However the very next day, The Holy Prophet Mohammad Al-Mustafa(pbuh&hf), again told the devout and faithful young Ali to do exactly as he had done the previous day. So another similar meal was prepared by Ali and everything went exactly as before, except that this time The Holy Prophet(pbuh&hf) was on his guard and made sure of addressing them.
For the 1st Time
"O sons of Abd Al-Muttalib. I know of no Arab who hath come to his people with a nobler Message than mine. Bringing you the best of this world and the next. God hath commanded me to call you unto Him. Which of you, then, will help me in this, and be my brother, my executor, and my successor amongst you?"
However there was just silence throughout the whole Clan. And each looked to each other. Anyone could have spoken up. But when the silence remained unbroken, the thirteen year old boy Ali Ibin Abe Taleb(as), jumped up and spoke, and said,
"O Prophet of God, I will be thy helper in this!"
The Holy Prophet smiled and gently asked Ali to sit down and again turned to the elders before Him and repeated for the second time.
Again for the 2nd Time
"O sons of Abd Al-Muttalib. God hath commanded me to call you unto Him. Which of you, then, will help me in this, and be my brother, my executor, and my successor amongst you?"
Again there was a deafening silence and again each looked for the other response, but none moved and once again Ali sprang to his feet and declared,
"O Prophet of God, I will be thy helper in this!"
The Holy Prophet smiled and looked around at each of the men sitting before him, and he then reluctantly gestured for Ali again to sit down, and he once agian started to repeat for the third time,
And again for the 3rd Time
"O sons of Abd Al-Muttalib. God hath commanded me to call my nearest of my kin unto Him, and I invite any of to join me. So I ask thee, which of you, then, will help me in this, and be my brother, my executor, and my successor amongst you?"
Again there was no response from the people gathered, and once again Ali sprang to his feet for the third time and declared,
"O Prophet of God, Let me, be thy helper, your brother, your executer and your successor!"
The Holy Prophet Mohammad Al-Mustafa(pbuh&hf) looked about him, and then gently laid his holy right hand on top of Ali's head and declared,
"Then Ali is my Helper, my Brother, my Executor and my Successor amongst you. Hearken unto him, and obey him."
Most of the startled men of Qurayshall rose to their feet, laughing and teasing Abu Taleb led by his own brother Abu Laheb, by saying to him,
"He hath ordered thee, to hearken unto thy son and to obey him.!"
Ignoring Abu Laheb's jeer. Zayd the devouted slave and adopted son of The Prophet and also the equally devouted Jafar Ali's elder brother quickly rose with other devoutees, warmly congratulating The Holy Prophet, and his young devoted cousin Ali, and now his Brother, his Executor and his Successor, and his father the clan chief of Bani Hashim, Abu Taleb(as).
source : www.al-shia.org