Since Ali was a member of the Prophet’s own family, he was inevitably the first, among males, to receive the message of Islam. He testified that God was One, and that Muhammad was His messenger. And he was very eager to stand behind Muhammad Mustafa to offer prayers. Since then Muhammad was never seen at prayer except when Ali was with him. The boy also memorized the verses of Al-Qur’an al-Majid as and when they were revealed to Muhammad. In this manner, he literally grew up with Qur’an. In fact, Ali and Qur’an “grew up” together as “twins” in the house of Muhammad Mustafa and Khadija-tul-Kubra. Muhammad Mustafa, the Messenger of Allah, had found the first Muslima in Khadija, and the first Muslim in Ali ibn Abi Talib.
Muhammad ibn Ishaq
Ali was the first male to believe in the Apostle of God, to pray with him and to believe in his divine message, when he was a boy of ten. God favored him in that he was brought up in the care of the Apostle before Islam began. (The Life of the Messenger of God)
Muhammad Husayn Haykal
Ali was then the first youth to enter Islam. He was followed by Zayd ibn Harithah, Muhammad’s client. Islam remained confined to the four walls of one house. Besides Muhammad himself, the converts of the new faith were his wife, his cousin, and his client. (The Life of Muhammad, Cairo, 1935)
The first of all his (Muhammad’s) converts was his wife, Khadija; the second his first cousin Ali, whom he had adopted; the third his servant Zeyd, a former slave. (Introduction to the Translation of Holy Qur’an, Lahore, Pakistan, 1975)
The third “witness” who accepted Islam, was Zayd ibn Haritha, the freedman of Muhammad, and a member of his household.
Zaid was one of the first to accept Islam, in fact the third, after Khadija and Ali. (Mohammed, the Man and his Faith, 1960)
Ali ibn Abi Talib was the first male to accept Islam, and his precedence is beyond any question. Allama Muhammad Iqbal, the poet-philosopher of Indo-Pakistan, calls him, not the first, but “the foremost Muslim.”
From Yahya b. al-Ash’ath b. Qays al-Kindi from his father, from his grandfather Afiif: Al-Abbas b. Abdul Muttalib was a friend of mine who used to go often to the Yaman to buy aromatics and sell them during the fairs. While I was with him in Mina, there came a man in the prime of life and performed the full rites of ablution and then stood up and prayed. Then a woman came out and did her ablution and stood up and prayed. Then out came a youth just approaching manhood, did his ablutions, then stood up and prayed by his side. When I asked Al-Abbas what was going on, and he said that it was his nephew Muhammad b. Abdullah b. Abdul Muttalib, who alleges that Allah has sent him as an Apostle; the other is my brother’s son, Ali ibn Abi Talib, who has followed him in his religion; the third is his wife, Khadija daughter of Khuwaylid who also follows him in his religion. Afiif said after he had become a Muslim and Islam firmly established in his heart, ‘Would that I had been a fourth.!’ (The Life of the Messenger of God)
The fourth witness who accepted Islam, was Abu Bakr, a merchant of Makkah. In the beginning, Muhammad preached Islam secretly for fear of arousing the hostility of the idolaters. He invited only those people to Islam who were known to him personally. It is said that through the efforts of Abu Bakr, the fourth Muslim, a few other Makkans also accepted Islam. Among them were Uthman bin Affan, a futurekhalifa of the Muslims; Talha, Zubayr, Abdur Rahman bin Auf, Saad bin Abi Waqqas, and Obaidullah ibn al-Jarrah.
For a long time the Muslims were very few in number and they did not dare to say their prayers in public. One of the early converts to Islam was Arqam bin Abi al-Arqam, a young man of the clan of Makhzoom. He was well-to-do and lived in a spacious house in the valley of Safa. Muslims gathered in his house to offer their congregational prayers. Three years passed in this manner. Then in the fourth year, Muhammad was commanded by God to invite his own folks to Islam openly.
And admonish thy nearest kinsmen. (Chapter 26; verse 214)