Musannaf Ibn Abi Shayba 3:2333

Abu Bakr narrated to us, he said: Ali bin Hashim narrated to us, from Ibn Abi Layla, from al-Hakam, from Miqsam, from Ibn Abbas, he said: If you are in the prayer, do not wipe your forehead, and do not blow, and do not move the pebbles.