Musnad Ahmad 329:44

'Ali ibn Bahr narrated to us, he said: al-Darawardi narrated to us, from 'Umarah ibn Ghaziyah, from 'Abbad ibn Tamim, from 'Abdullah ibn Zayd: "That the Messenger of Allah, may Allah bless him and grant him peace, went out to the prayer ground (musalla) to seek rain, and he was wearing a black khamisah (a square garment). He took hold of its lower part to make it its upper part, but it was heavy for him, so he turned it over onto his shoulders."