Sahih al-Bukhari 24:39
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 24:39
In-book reference
Book 24, Hadith 39
Arabic Text
حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مُحَمَّدٍ، حَدَّثَنَا هِشَامٌ، حَدَّثَنَا مَعْمَرٌ، عَنِ الزُّهْرِيِّ، عَنْ عُرْوَةَ، عَنْ حَكِيمِ بْنِ حِزَامٍ ـ رضى الله عنه ـ قَالَ قُلْتُ يَا رَسُولَ اللَّهِ أَرَأَيْتَ أَشْيَاءَ كُنْتُ أَتَحَنَّثُ بِهَا فِي الْجَاهِلِيَّةِ مِنْ صَدَقَةٍ أَوْ عَتَاقَةٍ وَصِلَةِ رَحِمٍ فَهَلْ فِيهَا مِنْ أَجْرٍ فَقَالَ النَّبِيُّ صلى الله عليه وسلم " أَسْلَمْتَ عَلَى مَا سَلَفَ مِنْ خَيْرٍ ".