Ibn Abbas (may Allah be pleased with them both) said that the Prophet (peace and blessings be upon him) said: "None of you should look at the private part of his wife, nor of his slave woman, when he has intercourse with her, for that causes blindness."
Abu Ahmad ibn Adi said: It seems that between Baqiyyah and Ibn Jurayj in this hadith there are some unknown or weak narrators, except that Hisham bin Khalid said: from Baqiyyah: Ibn Jurayj narrated to me.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13540