Musnad Ahmad 1156:226

Waki’ narrated to us, Sufyan narrated to us, from ‘Abdullah ibn ‘Uthman ibn Khuthaym, from ‘Abd al-Rahman ibn ‘Abdullah ibn Sabit, from Hafsah bint ‘Abd al-Rahman, from Umm Salamah, who said: When the Emigrants (Muhajirun) arrived in Medina to the Helpers (Ansar), they married their women. The Emigrants used to practice *jaba* (sexual intercourse in a specific position), while the Helpers did not practice *jaba*. A man from the Emigrants desired his wife for that, but she refused him until she asked the Prophet, peace and blessings of Allah be upon him. She went to him, but she was too shy to ask him, so Umm Salamah asked him. Then it was revealed: "Your wives are a tilth for you, so come to your tilth when or how you will" [Al-Baqarah: 223]. And he said: "No, except in one passage (womb)." And Waki’ said: "Ibn Sabit is a man from Quraysh."