Hazrat Ali Ibn Abi Talib (May Allah be pleased with him) was the next to enter in the fold of Islam after Hazrat Khadija R.A.
He was then a youth of ten years, and had been brought up under the guardianship of the Prophet peace be upon him since his early childhood.
The Prophet S.A.S had taken the charge of Hazrat Ali (May Allah be pleased with him) from his uncle Abu Talib,
and kept him as a member of his family since the time a grievous famine befell Quraysh. (Ibn Hisham, Vol. I, p. 245)
FIRST MALE TO ACCEPT ISLAM
When the Holy Prophet (Sallallahu ‘alaihi we Salaam) started getting revelations, Hadrat Ali (R.A.) was about ten years old.
The Holy Prophet (Sallallahu ‘alaihi we Salaam) disclosed his mission before Ali and he accepted it immediately, thus he became the first youth to enter the fold of Islam.
When the Holy Prophet (Sallallahu ‘alaihi we Salaam) started to preach openly, he invited all of his family members to a feast and announced his mission before them.
Nobody listened to him, but young Ali stood up and said. “Though my eyes are sore, my legs are thin and I am the youngest of all those present here yet I will stand by you, 0h Messenger of Allah.”
Hearing this all the leaders of Quraish laughed but Ali proved his words to be true after supporting the Holy Prophet (Sallallahu ‘alaihi we Salaam) in his mission from the beginning till the end.