Sunan Ibn Majah, Chapter: The Chapters on Divorce

"We were in the mosque one Friday night when a man said: 'If a man finds a man with his wife and kills him, will you kill him, and if he speaks,will you flog him. By Allah I will mention that to the Prophet (saw). So he mentioned that to the Prophet (saw), and Allah revealed the Verses of Li'an. Then after that the man came and accused his wife, so the Prophet (saw) told them to go through the procedure of Li'an and he said: 'Perhaps she will give birth to a black child.’ Then she gave birth to a black child with curly hair."