Sahih Muslim Book 8, Hadith Number 3389.

Chapter: It is forbidden to have intercourse with a pregnant slave woman.

Abu Darda’ (Allah be pleased with him) related from the Prophet of Allah (May peace be upon him) that he came upon a woman who was in the advanced stage of pregnancy at the door of a tent. He (the Holy Prophet) said: Perhaps he (the man accompanying her) intends to cohabit with her. They said: Yes. Thereupon Allah’s Messenger (May peace be upon him) said: I have decided to curse him with such a curse as may go along with him to his grave. How can he own him (the child to be born) and that is not lawful for him, and how can he take him as a servant for that is not lawful for him?