Sahih Muslim Book 1, Hadith Number 224.

Chapter : Pertaining to the virtuous act of a man before embracing Islam.

It is narrate on the authority of Hakim b. Hizam: I said: Messenger of Allah, I did so some of the deeds in the state of ignorance. (One of the transmitters Hisham b. Urwa explained them as acts of piety. Upon this the Messenger, of Allah remarked: You have embraced Islam with all the previous acts of virtue. I said: By God, I would leave nothing undone in Islam the like of which I did in the state of ignorance.