Ibn Umar saw me playing with pebbles during the prayer. When he finished, he forbade me from doing so and said, "Do as the Messenger of Allah ﷺ used to do."I asked, "And how did he do it?"He replied, "When he sat during the prayer, he would place his right palm on his thigh and close all of his fingers, pointing with the finger next to the thumb, and he would place his left palm on his left thigh."
أخبرنا قتيبة بن سعيد عن مالك عن مسلم بن أبي مريم
رآني ابن عمر وأنا أعبث بالحصى في الصلاة فلما انصرف نهاني وقال اصنع كما كان رسول الله ﷺ يصنع قلت وكيف كان يصنع قال كان إذا جلس في الصلاة وضع كفه اليمنى على فخذه وقبض يعني أصابعه كلها وأشار بإصبعه التي تلي الإبهام ووضع كفه اليسرى على فخذه اليسرى