Sayyiduna Ibn Abbas (may Allah be pleased with them both) narrates that some people of (the tribe of) Himyar came to the Prophet (peace and blessings be upon him) and asked him (peace and blessings be upon him) about certain matters. A man among them said: I love women, and I would like to come to my wife while she is bent forward (from behind), so what is your view about that? Thereupon Allah, the Mighty and Majestic, revealed this verse: "Your wives are a tilth for you, so come to your tilth however you wish" [Surah al-Baqarah: 223]. Then the Messenger of Allah (peace and blessings be upon him) said: "Come to her from the front or from behind, provided that it is in the private part (the vagina)."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 12927