Hadith: The Jews used to say: If one has sexual intercourse with his wife from her back, then she will deliver a squint-eyed child. So this verse was revealed: {Your wives are a place of sowing of seed for you, so come to your place of cultivation however you wish} [Sūrat al-Baqarah: 223]

عن جابر رضي الله عنه قال: "كانت اليهود تقول: إذا جَامَعَها مِن وَرَائِها جاء الولد أَحْوَلَ، فنزلت: {نِسَاؤُكُمْ حَرْثٌ لَكُمْ فَأْتُوا حَرْثَكُمْ أَنَّى شِئْتُمْ}، [البقرة: 223]".
[صحيح] - [متفق عليه]

Jābir (may Allah be pleased with him) reported: The Jews used to say: "If one has sexual intercourse with his wife from her back, then she will deliver a squint-eyed child." So this verse was revealed: {Your wives are a place of sowing of seed for you, so come to your place of cultivation however you wish.} [Sūrat al-Baqarah: 223]
[Authentic hadith] - [Narrated by Bukhari & Muslim]

Explanation

The Jews used to be strict regarding the positions of sexual intercourse without any knowledge to support that. The Aws and Khazraj tribes used to follow their sayings and actions because they were People of the Book. An example of their false beliefs is their claim that if a man had sexual intercourse with his wife in her vagina from her back, any child destined to be born out of this intercourse would be squint-eyed. Hence, Allah, the Exalted, revealed the following verse: {Your wives are a place of sowing of seed for you, so come to your place of cultivation however you wish} [Sūrat al-Baqarah: 223]. This verse refutes their claim and shows that Allah permits this position as long as it is done in the vaginal passage.