Fiqh-us-Sunnah Volume 1, Purification and Prayer, Fiqh 1.111B.

Says ‘Aishah, “The Prophet was sitting with his thigh exposed when Abu Bakr asked, and received, permission to enter. The same thing happened with ‘Umar. However, when ‘Uthman sought permission to enter, the Prophet covered himself with his clothes. When they left, I said, ‘O Messenger of Allah, you permitted Abu Bakr and ‘Umar to enter while your thigh was exposed. When ‘Uthman asked permission to enter, you covered yourself with your clothes.’ He said, ‘O ‘Aishah, should I not be shy of a man who, by Allah, even the angels are shy of’?” (Related by Ahmad and al-Bukhari in mu’allaq form.)

Says Anas, “During the battle of Khaibar, the Prophet’s gown was withdrawn from his thigh until I could see its whiteness.” (Related by Ahmad and al-Bukhari.)

Says Ibn Hazm, “It is correct to say that the thigh is not part of the ‘aurah. If it were so, why would Allah allow His Prophet, who is protected (from sin), to uncover his so that Anas and others could see it? Allah would have kept him from doing this. According to Jabir as recorded in the two Sahihs, when the Prophet was young (before his prophethood), he was one time carrying the stones of the Ka’bah, wearing only a loincloth. His uncle al-‘Abbas said to him, ‘O nephew, why don’t you untie your waistcloth and put it on your shoulder for padding?’ The Prophet did so and fell unconscious. He was never seen naked again after that.”‘

Muslim records from Abu al-‘Aliya that ‘Abdullah ibn as-Samit struck his thigh and said, “I asked Abu Zharr, and he struck my thigh as I struck yours, and he said, ‘I asked the Messenger of Allah, upon whom be peace, and he struck my thigh as I have struck yours and said, ‘Perform the prayer in its time…” Ibn Hazm said, “If the thigh was ‘aurah, why would the Messenger of Allah touch it?” If the thigh was ‘aurah according to Abu Zharr, why would he have struck it with his hand? The same can be asked for ‘Abdullah ibn as-Samit and Abu al-‘Aliya. It is not allowed for a Muslim to strike with his hand another man’s pubic area, or the clothes over the pubic area. Nor can a man touch the clothing over a woman’s ‘a urah.

Ibn Hazm mentions that Hubair ibn al-Huwairith looked at Abu Bakr’s thigh when it was uncovered, and that Anas ibn Malik came to Qas ibn Shamas when his thigh was uncovered.

However, the following hadith are used to show that the thighs and so on are part of the ‘aurah:

Reported Muhammad Jahsh, “The Messenger of Allah, upon whom be peace, passed by Ma’mar while his thighs were uncovered. He said, to him, ‘O Ma’mar, cover your thighs, for they are (part of the) ‘aurah.” This is related by Ahmad, al-Hakim and al-Bukhari in Tareekh and in mu’allaq form in his Sahih.

Reported Jurhad, “The Messenger of Allah passed by me when the cloak I was wearing did not cover my thigh. He said, ‘Cover your thigh, for it (is part of the) ‘aurah.” This is related by Ahmad, Abu Dawud and at-Tirmizhi, who called it hassan, and by al-Bukhari in mu’allaq form in the Sahih.