Musannaf Ibn Abi Shayba 9:689

Yahya ibn Sa'id narrated to us, from Mas'ud ibn 'Ali, who said: I said to 'Ikrimah, "Inform me about practicing *'azl* (coitus interruptus) with a slave girl of mine." He said, "She is your tillage; so if you wish, make her thirsty, and if you wish, irrigate her."