From Sahih Muslim (Hadith 3536):
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 ti'Ith; go then unto your tilth, as you may desire
Reference: Muslim 3536