Sayyidah Umm Salamah (may Allah be pleased with her) said: A woman came to ask the Prophet (peace and blessings be upon him) about her husband, who would have intercourse with his wife lying face down. When the Prophet (peace and blessings be upon him) came, she felt shy. He (peace and blessings be upon him) asked about her, and Umm Salamah (may Allah be pleased with her) informed him; he (peace and blessings be upon him) said: "Send her to me." Then he (peace and blessings be upon him) recited this verse: "Your wives are a tilth for you, so come to your tilth however you wish." [Surah al-Baqarah: 223] "The man may come from the front or from behind, but into the one opening."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 14106