Musnad Abu Ya'la al-Mawsili 108:44

Abu al-Rabi' narrated to us, Hafs ibn Abi Dawud narrated to us, from Muhammad ibn Abd al-Rahman, from 'Ata', from Jabir ibn Abd Allah, who said: The Messenger of Allah (may Allah bless him and grant him peace) visited a sick person while I was with him. He saw him praying and prostrating upon a pillow, so he forbade him and said: "If you are able to prostrate upon the ground, then prostrate; otherwise, gesture with a gesture, and make the prostration lower than the bowing."