Musnad Abu Ya'la al-Mawsili 2:83

Ishaq ibn Abi Isra'il narrated to us, Abd al-Razzaq narrated to us, Ma'mar narrated to us, from al-Zuhri, from Ubayd Allah ibn Abd Allah ibn Abi Thawr, from Ibn Abbas, from Umar ibn al-Khattab, who said: I entered upon the Messenger of Allah (may Allah bless him and grant him peace), and he was reclining on a mat of reeds which had left an impression on his side. I raised my head in the house, and by Allah, I did not see anything in it that would catch the eye, except for three hides.