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.'" (PT)
English reference (PT): Vol. 5, Book 41, Hadith 2795 (PT)
Arabic reference (PT): Book 43, Hadith 3025 (PT)