Musannaf Ibn Abi Shayba 3:5116

Sufyan narrated to us, from al-Hasan ibn Ali, who said: I saw Ibn Mughaffal spitting in the mosque. And my grandmother was an *umm walad* (a slave woman who bore a child) to al-Hasan ibn Ali, and he used to practice *‘azl* (coitus interruptus) with her.