Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) said concerning the saying of Allah Almighty: "And let them not display their adornment except what is apparent of it" [Surah al-Nur: 31]: The apparent adornment is the face, the kohl of the eye, the henna of the hand and the ring; this she may show in her house to whoever enters upon her. Then He said: "And let them not display their adornment except to their husbands, or their fathers, or their husbands' fathers, or their sons, or their husbands' sons, or their brothers, or their brothers' sons, or their sisters' sons, or their women, or those whom their right hands possess, or male attendants who have no desire" [Surah al-Nur: 31]. The adornment she may display to these people is her two earrings, her necklace and her two bracelets. As for her anklets, her armlet, her upper chest and her hair, she does not display them except to her husband.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13537
Bahz bin Hakim narrates from his father, from his grandfather (may Allah be pleased with him), who said: I said: O Messenger of Allah (peace and blessings be upon him)! Regarding our private parts, what may we expose and what must we cover? He (peace and blessings be upon him) said: "Guard your private parts except from your wife and your slave woman." I said: What do you think if we are among one another? He said: "If you are able to ensure that no one sees it, then let no one see it." Then I said: What if one of us is alone? He (peace and blessings be upon him) said: "Allah Almighty is more deserving than people that one should feel shy before Him."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13538
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