Muwatta Malik 1472

وَحَدَّثَنِي مَالِكٌ، أَنَّهُ بَلَغَهُ عَنِ الْمَقْبُرِيِّ، أَنَّهُ قَالَ سُئِلَ أَبُو هُرَيْرَةَ عَنِ الرَّجُلِ، تَكُونُ عَلَيْهِ رَقَبَةٌ هَلْ يُعْتِقُ فِيهَا ابْنَ زِنًا فَقَالَ أَبُو هُرَيْرَةَ نَعَمْ ذَلِكَ يُجْزِئُ عَنْهُ ‏.‏

Malik related to me that he had heard that al-Maqburi said that Abu Hurayra was asked whether a man who had to free a slave, could free an illegitimate child to fulfil that obligation. Abu Hurayra said, "Yes. That will give satisfaction for him

Reference

Muwatta Malik 1472

In-book

Book 38, Hadith 9