Sayyiduna Muhammad bin Abdullah bin Jahsh (may Allah be pleased with him) said: I was with the Messenger of Allah (peace and blessings be upon him) when he (peace and blessings be upon him) passed by Ma'mar, who was sitting near his house in the market with his thighs uncovered. The Prophet (peace and blessings be upon him) said: "O Ma'mar! Cover your thighs, for both thighs are 'awrah (to be covered)."
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 16599