When a man has intercourse with his wife through the vagina but being on her back. the child will have squint, so the verse came down:" Your wives are your tilth; go then unto your tilth as you may desire" (ii. 223) (Using translation from Muslim 1435a)
كَانَتِ الْيَهُودُ تَقُولُ مَنْ أَتَى امْرَأَتَهُ فِي قُبُلِهَا مِنْ دُبُرِهَا كَانَ الْوَلَدُ أَحْوَلَ فَنَزَلَتْ {نِسَاؤُكُمْ حَرْثٌ لَكُمْ فَأْتُوا حَرْثَكُمْ أَنَّى شِئْتُمْ} [البقرة 223]