Musannaf Ibn Abi Shayba 9:767

'Abbad ibn al-'Awwam narrated to us, from al-Husayn, from Murrah al-Hamdani, that some of the Jews came to some of the Muslims and said: "You approach women from behind them." He said: "It is as if he disliked the kneeling position (al-ibrak)." He said: "So they mentioned that, and this verse was revealed: 'Your wives are a tilth for you, so come to your tilth when or how you will.' So Allah granted a concession to the Muslims to approach women in the private parts however they wished, from in front of them, and if they wished, from behind them."