Abdullah bin Umar saw me fiddling with pebbles during the prayer. When I had finished, he forbade me from doing so and said, "Do as the Messenger of Allah ﷺ used to do."I asked, "How did the Messenger of Allah ﷺ do it?"He replied, "When he sat during the prayer, he would place his right palm on his right thigh, close all his fingers, and point with the finger next to the thumb. He would place his left palm on his left thigh. This is how the Messenger of Allah ﷺ used to do it."
رآني عبد الله بن عمر، وأنا أعبث بالحصباء في الصلاة، فلما انصرفت نهاني وقال: اصنع كما كان رسول الله ﷺ يصنع، فقلت: وكيف كان رسول الله ﷺ يصنع؟ قال: كان إذا جلس في الصلاة وضع كفه اليمنى على فخذه اليمنى، وقبض أصابعه كلها، وأشار بإصبعه التي تلي الإبهام، ووضع كفه اليسرى على فخذه اليسرى، وقال: هكذا كان رسول الله ﷺ يفعل.
Malik narrated it in "Prayer" (48) from Muslim bin Abu Maryam, from Ali Ibn Abdul-Rahman Muawi, in the same manner. Muslim narrated it in "Mosques" (116/580) from Yahya bin Yahya, who said, "I read it to Malik," in the same manner.