Musnad Ahmad 1153:1136

Narrated to us Abd al-Rahman, from Abdullah ibn Umar, from his brother, from al-Qasim, from Aisha: That Gabriel, peace be upon him, came to the Prophet, may Allah bless him and grant him peace, upon a pack horse, and upon him was a turban, the end of which was between his shoulders. So I asked the Prophet, may Allah bless him and grant him peace, and he said: "Did you see him? That was Gabriel, peace be upon him."