Musnad Ahmad 33:1021

Hassan narrated to us, Zuhair narrated to us, from Abu al-Zubayr, from Jabir: "That the Messenger of Allah (peace and blessings of Allah be upon him) used to pray in a single garment, wrapping himself in it." Some of the people said to Abu al-Zubayr, while I was listening: "The obligatory prayer?" He said: "The obligatory prayer, and other than the obligatory prayer."