Ten years after the birth of Ali (A.S.), the Prophet (S.A.W.W.) was ordered to reveal his Prophethood. All sects of Islam are in agreement on the fact that Ali (A.S.) was the first to testify to the Prophethood, followed by Lady Khadijah (S.A.).
For three years, the Holy Prophet (S.A.W.W.) was preaching Islam under absolute secrecy, at the end of the third year of his mission, he received orders to preach to his near relations and to admonish them.
DAWAT-E-ZUL-ASHEERAH
(Dinner for the Relatives)
The Holy Prophet directed Ali (A.S.) to prepare a dinner gathering at Hazrat Abu Talib’s (A.S.) house and to invite the sons and grandsons of Hazrat Abdul Muttalib (A.S.). This was done and about forty of them came but Abu Lahab (L.A.) made the company break up before Muhammad (S.A.W.W.) had an opportunity to speak.
Next day, a second invitation was issued. When they came and the meal was served, the Holy Prophet (S.A.W.W.) rose but was again interrupted by Abu Lahab (L.A.). This time, however, Hazrat Abu Talib (A.S.) put his hands on Abu Lahab’s (L.A.) shoulders and forced him to sit down and shut up.
Muhammad (S.A.W.W.) then declared his sacred character, offered the treasures of time and of eternity to whomsoever should become his disciples, and concluded by demanding, “Who among you will aid me to bear this burden, who will be my Vicegerent, Heir and Caliph, as Aaron was unto Moses?”
The assembly remained mute with astonishment, not one venturing to accept the offered perilous office, until Ali (A.S.), Muhammad’s (S.A.W.W.) cousin, stood up and exclaimed, “O Prophet! I will, though I am indeed the youngest of those present, the most rheum of them as to the eyes, and the slenderest of them as to the legs.”
On this, locking his arms around the generous and courageous youth, and pressing him to his chest, Muhammad (S.A.W.W.) declared: “Behold my Brother, my Vicegerent, my Heir and my Caliph, and obey him.”
Sources: Al Murtuza, page 9 - Hafiz Abdul Rahman
Muallim-ut-Tanzil
Abu Fida
Nasayi
Allama ibne Ashar
Tags: abu lahab, abu talib, ali, brother, caliph, heir, muhammad, relatives, vicegerent, zul ashira
Certainly not a preacher, certainly not one to back down from the defense of the Ahle Bayt (A.S.) and certainly not one to provoke arguments over sectarian differences on purpose. 
If you would like to discuss, sure no problem.
Beware UTP! He’s working for Mushy …. he’ll enlighten you no end! 
Oh my son! This world is like an ocean in which many a creation had drowned. Make, therefore, the fear of God your boat in this ocean; your faith the main hull of the boat; reliance on God as its sails; reason as its rower; knowledge as its captain; and patience as its anchor.
Hazrat Ali (A.S.)
Credit: Wajahat Abbas
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