It is narrated from the grandson of Sayyiduna Jarhad (may Allah be pleased with him), from his grandfather, who said: the Prophet (peace and blessings be upon him) passed by me while I was in the mosque, wearing a cloak from which my thigh had become uncovered, and the Prophet (peace and blessings be upon him) said: "O Jarhad, cover your thigh, for the thigh is awrah."
Hadith Referenceالمعجم الكبير للطبراني / باب الجيم / 2133