(24) باب مَنْ تَصَدَّقَ فِي الشِّرْكِ ثُمَّ أَسْلَمَ
Narrated Hakim bin Hizam:
I said to Allah's Messenger (ﷺ), "Before embracing Islam I used to do good deeds like giving in charity, slave-manumitting, and the keeping of good relations with Kith and kin. Shall I be rewarded for those deeds?" The Prophet (ﷺ) replied, "You became Muslim with all those good deeds (Without losing their reward)."
Reference: Sahih al-Bukhari 1436
In-book reference: Book 24, Hadith 39
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 2, Book 24, Hadith 517