Abu Dawud Book 6, Hadith Number 2267.

Narated By Abdullah ibn Amr ibn al-‘As : A man got up and said: Apostle of Allah, so-and-so is my son; I had illicit intercourse with his mother in the pre-Islamic period. The Apostle of Allah (PBUH) said: There is no unlawful claiming of paternity in Islam. What was done in pre-Islamic times has been annulled. The child is attributed to the one on whose bed it is born, and the fornicator is deprived of any right.