Musnad Ahmad 1007:24

Waki’ narrated to us, Abu al-Umays narrated to us, from ‘Amir—meaning Ibn ‘Abd Allah ibn al-Zubayr—from al-Zurqi, from Abu Qatadah, that the Prophet, peace and blessings of Allah be upon him, used to: "When he sat in the prayer, he would place his right hand upon his right thigh, and he would gesture with his finger."