Sahih Muslim Book 8, Hadith Number 3364.

Chapter: Permissibility of having sexual intercourse with one’s wife from the front or from behind avoiding the anus.

Jabir (b. Abdullah) (Allah be pleased with him) reported that the Jews used to say that when one comes to one’s wife through the vagina, but being on her back, and she becomes pregnant, the child has a squint. So the verse came down: “Your wives are your tilth; go then unto your tilth, as you may desire.”