Mukhtasar Bukhari

It is narrated from Sayyiduna Sa’d bin Abi Waqqas (may Allah be pleased with him) that his son Mus’ab prayed beside him. (Mus’ab) says: I joined both my palms together and then pressed them between my knees, so my father forbade me and said: We used to do this, but we were forbidden from it and were commanded to place our hands (in bowing) on our knees.