Narrated Abu Az-Zinad:
"Ibn Jarhad informed me from his father, that the Prophet (ﷺ) passed by him while his thigh was exposed, so the Prophet (ﷺ) said: 'Cover your thigh, for indeed it is 'Awrah.'" (JA)
English reference (JA): Vol. 5, Book 41, Hadith 2798 (JA)
Arabic reference (JA): Book 43, Hadith 3028 (JA)