The most amazing attribute Imam Ali (a.s.) holds is that he was born in the Holy Kabaah. The source; Shah Waliyullah in his book ‘Izaalatul Khifa’ mentions that the distinction of Imam Ali (as) is that no one was born before or will be born after him in the Ka’aba.
On the 13th of the month of Rajab, twenty-three years before the migration of the Prophet (P.B.U.H.) a child was born in the family of Abu Talib, the light of whom kindled the whole World. Kunaab Mecci narrates about his birth: “We and Abbas (Ibne Abdul Mutalib) were sitting together when suddenly we saw Fatima bint-e-Asad moving towards the Kaabah in the condition having delivery pain and saying “Oh God I have faith in you and the Prophet ( i.e., Abraham) who by your command laid the foundation of this house. O God! I swear you by the same Prophet (P.B.U.H.) and swear you by the child in my womb make this birth comfortable and easy for me.”
This was the time when all of us saw with our own eyes that the wall of Kaabah broke apart and Fatima bint-e-Asad entered into the Kaabah. Then the wall again united.
We ran terrified and trembling to our houses to send our women into the Kaabah for the help and assistance of Fatima. We did our best but the door did not open. This event surprised all the people of Mecca.
The women of Mecca were anxiously counting moments to meet Fatima till the time she came out of the Kaabah along with a beautiful baby, saying, “God has chosen me from among the ladies of Mecca and He made me His guest in His house and gave me meals and fruits of the heaven to eat.
The ladies who were surrounding her in the form of a circle and escorting her to her home asked her, “What name have you given to this child?”
She said: “When I was in the Kaabah, I heard a hidden voice call,” Name this child “ALI”.
Yes! We are talking about Ali (A.S.) the pious man whose childhood and infancy period lasted in such a pure and chaste way that he himself stated in Nahjul Balaghah, “The Prophet (P.B.U.H.) used to pick me in his lap and embrace me and chew the food and put it into my mouth.
Ali Ibne Abi Talib describes this enlightening period of his age as under: The Prophet (P.B.U.H.) used to go the Cave of Hira but nobody except he (P.B.U.H.) and I did know about it. At the time when the religion of Islam had not yet reached the homes, he ( P.B.U.H.) and his wife Khatija were the only Muslims. I was the next person to them who saw the light of revelation and prophet hood and smelled the fragrance of the Prophet hood.
When the Prophet (P.B.U.H.) of Islam was ordered by God to invite his family members to embrace Islam Ali ( A.S.) according to the advice of the Prophet (P.B.U.H.) invited forty persons of the Prophet’s family at his home. Although the food was quite little but all of them ate fully well. After the meal was over the Prophet (P.B.U.H .) spoke to those present saying, “Oh the sons of Abdul Mutalib, God has ordered me to invite you to embrace Islam and get you introduced to it.”
Whosoever, having believed in my Prophet hood, promises to help and assist me shall be my brother, deputy and successor and my caliph.
He repeated this sentence thrice but no one except “Ali (A.S.)” gave a positive response. As many time as the Prophet ( P.B.U.H.) addressed the persons present, nobody except Ali (A.S.) answered. Ali (A.S.) was rising again and again to his feet and promising help to him and announcing his faith.
Taken from http://www.duas.org/ImamAli.htm