Musannaf Ibn Abi Shaybah 8069 — Moving pebbles

A freed slave of Atiyyah said: I prayed beside Qays bin Ubad. During the prayer I took hold of a stick and put it to my mouth, so he struck my chin. When he had completed the prayer, I said to him: "Why did you do something that astonished me?" He said: "It used to be said that whoever does something idle in his prayer, his prayer is reduced by that much."