Musannaf Ibn Abi Shayba 9:766

Qabisah narrated to us, he said: Sufyan informed us, from Abdullah ibn Uthman ibn Khuthaym, from Ibn Sabit, from Hafsa, from Umm Salama, who said: When the Emigrants (Muhajirun) arrived in Medina, they married among the Helpers (Ansar). They used to practice *jabu* (coitus interruptus), while the Helpers did not do that. A woman among them said to her husband, "I will ask the Messenger of Allah (peace be upon him)." She felt shy to ask him, so I asked him. He called her and recited to her: "Your wives are a tilth for you, so come to your tilth when or how you will," in a single passage.