Musannaf Ibn Abi Shayba 3:5479

Waki' narrated to us, he said: Sufyan narrated to us, from Ma'mar ibn 'Abd al-Rahman, he said: I prayed beside a man from the companions of 'Abdullah, and I touched the pebbles. When he prayed, he said: 'Abdullah said: "Let not one of you ask his Lord for anything of good while the stone is in his hand."