The Holy Prophet(pbuh) made this announcement about Imam Ali(as) since his first invitation to Islam " You are my brother, you are my special one, and you are my deputy”..
English Translation:
Rabia bin Najid narrated:
One person said to Ali ibn Abi Talib “Oh commander of the believers, how come you are the inheritor of your cousin (Prophet Muhammad) instead of your uncle? “
Commander of believer (Ali) said:
“Holy Prophet gathered all the children of Abdul Mutalib and prepared small amount of food for them (MUDD) but everybody got full with the food still that food was remaining in the same amount which prophet made for them.
It seems like nobody touched that food. Then the Holy Prophet order for a bowl of water, everybody drank water very well from that bowl but it looks like nobody drink that water and it was in the same quantity.
Then Holy Prophet said:
“Oh children of Abdul Mutalib, I am sent down to the people especially for you people…. Who will give his oath of allegiance to me? That person would be my brother, my special one, my inheritor and my deputy”.
Nobody stood up from those people then I came forward even I was the youngest one. Then the Holy Prophet said:
“O Ali, sit down”
Holy prophet repeated his announcement 3 times I was the one who used to stand up but the prophet always tell me to sit down.
Then the holy prophet said it for the third time (I stood up) the prophet put his hand on my hand then said
“You are my brother, you are my special one, and you are my deputy”
That is why I am the inheritor and successor of my cousin (Prophet Muhammad (pbuh).
Part B
Part C
Part D