Musnad Ahmad 304:8

Ya'qub narrated to us, my father narrated to us, from Ibn Ishaq, who said: Yahya ibn Sa'id ibn Qays al-Ansari mentioned, from Abu Umamah ibn Sahl, from 'Umar ibn Abi Salamah, who said: "I have seen the Messenger of Allah, peace and blessings of Allah be upon him, praying in a single garment, having wrapped himself in it."