The Prophet, peace and blessings be upon him, said: "Cover your thigh, for it is part of the 'awrah." (1)
This is a good (hasan) hadith.

3005 - Wāṣil ibn ʿAbd al-Aʿlā narrated to us, Yaḥyā ibn Ādam narrated to us, from al-Ḥasan ibn Ṣāliḥ, from ʿAbd Allāh ibn Muḥammad ibn ʿAqīl, from ʿAbd Allāh ibn Jarhad al-Aslamī, from his father, from the Prophet, peace and blessings be upon him, who said: "The thigh is 'awrah." (2)
This is a good and rare (gharīb) hadith from this chain.

3006 - Wāṣil ibn ʿAbd al-Aʿlā al-Kūfī narrated to us, he said: Yaḥyā ibn Ādam narrated to us, Isrāʾīl narrated to us, from Abū Yaḥyā, from Mujāhid, from Ibn ʿAbbās, that the Prophet, peace and blessings be upon him, said: "The thigh is 'awrah." (3)
On this topic there is also [a hadith] from ʿAlī and Muḥammad ibn ʿAbd Allāh ibn Jaḥsh. (4)
This is a good and rare hadith.

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(1) It is a good hadith as the author stated, and it is in the Muṣannaf of ʿAbd al-Razzāq (19808), and from his chain Aḥmad narrated it (15929).
(2) It is good like the preceding one, and it is in the Musnad of Aḥmad (15930).
(3) It is a good hadith due to its supporting witnesses, and this chain is weak because of Abū Yaḥyā — who is al-Qattāt. It is in the Musnad of Aḥmad (2493), where its full documentation is found. It is supported by the hadith of Jarhad al-Aslamī mentioned before it.
(4) The hadith of ʿAlī was narrated by ʿAbd Allāh in his additions to the Musnad (1249), and the hadith of Muḥammad ibn ʿAbd Allāh ibn Jaḥsh is in the Musnad (22494), and it is a good hadith. That the thigh of a man is 'awrah that must be covered is the school of Aḥmad, al-Shāfiʿī, Abū Ḥanīfah, and Mālik, may Allah have mercy on them.