Musannaf Ibn Abi Shaybah

Ismail (may Allah have mercy on him) says that I asked Hazrat Ata (may Allah have mercy on him) what is the ruling if a mistress says to her slave, "I free you on the condition that you marry me?" He replied that it would have been better if she had simply freed him. I asked Hazrat Abdullah bin Ubaid bin Umair (may Allah have mercy on him) the same question, and he gave a similar answer as Hazrat Ata (may Allah have mercy on him). I asked Hazrat Mujahid (may Allah have mercy on him), and he became angry and said that this is an act punishable by Allah and the ruler.