Narrated Zur'ah bin Muslim bin Jardah Al-Aslami:
about his grandfather Jarhad, he said: "The Prophet (ﷺ) passed by Jarhad in the Masjid and his thigh was exposed, so he said: 'Indeed the thigh is 'Awrah.'" (JA)
English reference (JA): Vol. 5, Book 41, Hadith 2795 (JA)
Arabic reference (JA): Book 43, Hadith 3025 (JA)