Sahih al-Bukhari 4528Book 65, Hadith 51
حَدَّثَنَا أَبُو نُعَيْمٍ، حَدَّثَنَا سُفْيَانُ، عَنِ ابْنِ الْمُنْكَدِرِ، سَمِعْتُ جَابِرًا ـ رضى الله عنه ـ قَالَ كَانَتِ الْيَهُودُ تَقُولُ إِذَا جَامَعَهَا مِنْ وَرَائِهَا جَاءَ الْوَلَدُ أَحْوَلَ. فَنَزَلَتْ {نِسَاؤُكُمْ حَرْثٌ لَكُمْ فَأْتُوا حَرْثَكُمْ أَنَّى شِئْتُمْ}
Jews used to say: "If one has sexual intercourse with his wife from the back, then she will deliver a squint-eyed child." So this Verse was revealed:-- "Your wives are a tilth unto you; so go to your tilth when or how you will." (2.223)