Musannaf Ibn Abi Shayba 3:6050

Jarir narrated to us, from Mansur, from Rashid Abu Sa'd, from Sa'id ibn Abd al-Rahman ibn Abza, who said: When the Messenger of Allah (may Allah bless him and grant him peace) sat in the prayer, he would place his hand upon his thigh. He would point with his finger during the supplication.