It is narrated from Sayyidah Umm Salamah (may Allah be pleased with her); she said: When the Muhajirun came to Madinah, they wanted to have intercourse with their wives from behind, in their private parts, but the women disliked this. They came to Sayyidah Umm Salamah (may Allah be pleased with her) and told her about it, so she asked the Prophet (peace and blessings be upon him), and he (peace and blessings be upon him) said: "Your wives are a tilth for you, so approach your tilth however you wish" [Surah al-Baqarah: 223], but only in the one opening.
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 20139