Musannaf Ibn Abi Shayba 3:1563

Waki’ narrated to us, he said: ‘Abd al-Salam ibn Shaddad al-Jariri (al-Hariri) Abu Talut narrated to us, he said: Ghazwan ibn Jarir al-Dabbi narrated to us, from his father, who said: When ‘Ali stood in prayer, he would place his right hand upon the wrist of his left hand. He would remain like that until he bowed, whenever he bowed, unless he was adjusting his garment or scratching his body.