Al-Maqburi (may Allah have mercy on him) said that Sayyiduna Abu Hurayrah (may Allah be pleased with him) was asked about a man who is obliged to free a slave: may he free a child born of fornication? Sayyiduna Abu Hurayrah (may Allah be pleased with him) said: Yes.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأيمان / 19998