Musannaf Ibn Abi Shayba 19:690

Abu Bakr narrated to us, he said: Waki’ narrated to us, from Isma’il bin Muslim, he said: I asked ‘Ata’, ‘Abdullah bin ‘Ubayd bin ‘Umayr, and Mujahid about a woman who had a slave, and she wanted to manumit him on the condition that he marries her. ‘Ata’ and ‘Abdullah bin ‘Ubayd said: She should manumit him and not stipulate a condition upon him. Mujahid said regarding this: It is a punishment from Allah and from the authority; she must separate from him, and the prescribed punishment (hadd) must be carried out upon her.