Musnad Ahmad 30:3060

Waki’ narrated to us, he said: Al-‘Umari narrated to us, from Khubayb ibn ‘Abd al-Rahman, from Hafs ibn ‘Asim, from Abu Hurayrah, who said: "The Messenger of Allah (peace and blessings of Allah be upon him) forbade the *al-samma’* wrap, and that a man should sit in a single garment while having his private parts exposed to the sky."