Mishkat al-Masabih 13 Marriage كتاب النكاح 35

وَعَنْ مُحَمَّدِ بْنِ جَحْشٍ قَالَ: مَرَّ رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ عَلَى مَعْمَرٍ وَفَخذه مَكْشُوفَتَانِ قَالَ: «يَا مَعْمَرُ غَطِّ فَخِذَيْكَ فَإِنَّ الفخذين عَورَة» . رَوَاهُ فِي شرح السّنة

Muhammad b. Jahsh told that God’s Messenger came upon Ma’mar when his thighs were uncovered and said, “Cover your thighs, Ma’mar, for the thighs are private parts.” It is transmitted in Sharh as-sunna .