If we may have a cursory glance on the biography of Abu Talib, we will find that he supported Muhammad for full 40 years, and displayed sacrifice during last ten years of his life. The only factor which kept him so steadfast was his strong faith, which he had to keep secret in Mecca, exercising strict taqiya (precautionary dissimulation). According to "Sirat-i Halabiya" (1st vol., p. 390), Abu Talib said to his children at the time of his death that, "I recommend Muhammad to you, because he is the trusted one of Qoraish and truthful one of Arabia and possesses all the virtues. He has brought a religion, which has been accepted by the hearts, but the tongues have chosen to deny it on account of fear of taunts. Whosever follows him becomes prosperous of his faith. If death had given me some more time, I would have warded off all the dangers that came to him."
Imam Jafar Sadik, according to "Usul-i Kafi" (p. 244) had said: "Abu Talib was like the People of the Cave, who had faith in their hearts but pretended to be polytheists." In one laudatory poem about his nephew, Abu Talib had said, as quoted by "Majma'ul Bayan" (7th vol., p. 36) that, "Dont you know that we consider Muhammad to be a Prophet of Allah like Musa bin Imran and read about him in the earliest book." In sum, it is quite true that Abu Talib had never publicly announced to embrace Islam, and this is the principal cause that the historians have doubted his faith. When a mention was made about Abu Talib, Imam Zayn al-Abidin is reported to have said, "I wonder why people doubt the faith of Abu Talib, when a woman cannot continue her matrimonial alliance with a non-Muslim husband after she has embraced Islam, and Fatima bint Asad was amongst those women who embraced Islam at a very early stage and still remained his wife till he breathed his last."