Zur'ah bin Abd al-Rahman bin Jarhad narrated from his father, who was one of the People of the Suffah, that he said: the Messenger of Allah (peace and blessings be upon him) sat with us one day while my thigh was uncovered, and he (peace and blessings be upon him) said: "Cover yourself; do you not know that the thigh is awrah?"
Hadith Referenceالمعجم الكبير للطبراني / باب الجيم / 2132