It must be believed that the fore-fathers of our Holy Prophet and our Imams have always been Muslims. Not only that but most of them have been deputies. The reports about Abu Talib's Islam which have come down to us from the members of the Holy Prophet's House are indisputable and exact. His life account is also a proof of His Islam.
source : http://www.islamicecenter.com/e-library/logic_islamic_rules/logic_islamic_rules_makarem_subhani_03.html
