Musannaf Ibn Abi Shayba 9:1536

Waki’ narrated to us, from Isma’il bin Muslim, from ‘Ata’ and ‘Abdullah bin ‘Ubayd bin ‘Umayr: He said: "You emancipate him and do not stipulate conditions upon him." And Mujahid said regarding this: "It is a punishment from Allah and from the authority."