Musnad Abu Ya'la al-Mawsili 152:116

Abu Khaythama narrated to us, Jarir narrated to us, from Layth, from Abd al-Rahman ibn al-Aswad, from his father, from Abdullah, who said: I went out with the Messenger of Allah (peace and blessings of Allah be upon him) to relieve himself, and he relieved himself. Then he said: "Seek for me something with which I may clean myself, and do not bring me a bone or dung." He said: Then he performed ablution and stood to pray. I saw him whenever he bowed, he would bend—meaning he would clasp his hands and place them between his knees. Layth said: The *ha'il* (bone) is the bone.