Mu'jam Kabir Tabarani 11051 — I presented the Qur'an to Ibn Abbas

Mujahid (may Allah have mercy on him) said: I presented the Qur'an to Ibn Abbas (may Allah be pleased with them both) from its beginning to its end, stopping at every verse and asking him about it, until I reached this verse: "Your wives are a tilth for you, so come to your tilth however you wish" [Al-Baqarah: 223]. Ibn Abbas (may Allah be pleased with them both) said: "This clan of Quraysh used to lay women down in Makkah and enjoy them from the front and from behind (that is, they adopted different positions in intercourse). When they came to Madinah and married among the Ansar and wanted to do the same with them, the Ansari women disliked it and said: This is something that was not done before. The matter spread until it reached the Prophet (peace and blessings be upon him), and Allah, the Mighty and Majestic, revealed this verse concerning it: 'Your wives are a tilth for you, so come to your tilth however you wish,' that is, from the front, and if you wish, (from behind) in a kneeling position." What is meant by this is the very place from which the child is born, that is, it is being said: Come to the tilth from wherever you wish (that is, there is choice in the manner of intercourse, not in the place).
Then Ibn Abbas (may Allah be pleased with them both) said: Ibn Umar (may Allah be pleased with them both) said that it is about her back passage; Ibn Umar (may Allah be pleased with them both) was mistaken in this - may Allah forgive him - whereas the matter was actually as (described above).