Musnad Abu Ya'la al-Mawsili 110:104

Ali ibn al-Ja'd narrated to us, Abu Ja'far al-Razi informed us, from 'Amr ibn Dinar, from Tawus, from Ibn Abbas, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "I have been commanded to prostrate upon seven members, and I have been forbidden from tucking up a garment or hair."