Sahih Bukhari Volume 3, Book 46, Hadith Number 715.

Narated By Hisham : My father told me that Hakim bin Hizam manumitted one-hundred slaves in the pre-lslamic period of ignorance and slaughtered one-hundred camels (and distributed them in charity). When he embraced Islam he again slaughtered one-hundred camels and manumitted one-hundred slaves. Hakim said, “I asked Allah’s Apostle, ‘O Allah’s Apostle! What do you think about some good deeds I used to practice in the prelslamic period of ignorance regarding them as deeds of righteousness?’ Allah’s Apostle said, “You have embraced Islam along with all those good deeds you did.”