Although the actual completion of the faith of Islam took place on the 18th of Dhul Hijjah on the plains of Ghadeer, its spiritual completion took place in the month of Rajab with the birth of Ali ibne Abi Talib (AS).
The striking contrast behind Fatima binte Asad, the mother of Imam Ali and the period of pregnancy and delivery and that of Mariam binte Imran, the mother of Prophet Jesus (AS) are indeed very interesting. Yes, this one example shows us the greatness of Fatima binte Asad, her child and their lofty rank in the sight of Allah (SWT)!
The Qur'an relates that when Mariam was facing the pains of labour, she first decided to retreat to the house of worship. She was however 'forced' out of there and was told that the House of Allah is not a place to deliver a child! Therefore, she turned towards the East and secluded herself in the desert to give birth. However, when we research the ahaadith, we see that when Fatima binte Asad was about to deliver and had gone to the Ka'bah to perform the Tawaf and complain to Allah (SWT) about her pains and make supplication for ease, the Ka'bah actually split open, welcoming her inside! For a period of three days, she remained in this holy sanctuary, only coming out after the birth of her son, Ali ibne Abi Talib!
The Prophet was one of the first people to see the infant and to welcome him into the world. Indeed, this bond of brotherhood and assistance for one another continued until the departure of the Prophet from this transient world.
Being a true monotheist and one whose parents had never even bowed down to the statues present in the Ka'bah, when the official message of Islam came to the Prophet of Islam in the cave of Hira, there was no need for Ali to 'convert' or 'accept Islam'! This 'new' set of teachings was nothing other than the nature which Allah had created him with and thus, when the first words of Wahi came from the Prophet, he automatically acknowledged them.
All historians are unanimous that when the Bi'that of the Prophet took place and the message of Islam was limited to one house, that it was the Prophet, Ali and Lady Khadijah (AS) who performed their prayers in congregation (Jama'at).
For 23 long years, the continued support of Ali ibne Abi Talib to the Prophet of Allah continued on various fronts - within the family of believers; in the preserving of the Divine Revelation and on the battle front. No doubt, it is for these and other reasons that when Allah wanted to speak of his greatness, he referred to him as the 'soul of the Prophet'. "But whoever disputes with you in this matter after what has come to you of knowledge, then say: Come let us call our sons and your sons and our women and your women and ourselves and yourselves, then let us be earnest in prayer, and pray for the curse of Allah on the liars." (3:61)