Musannaf Ibn Abi Shayba 3:5442

Abu Bakr narrated to us, he said: Sufyan ibn ‘Uyaynah narrated to us, from al-Zuhri, from Abu al-Ahwas, from Abu Dharr. It was said to Sufyan: "From the Prophet, may Allah bless him and grant him peace?" He said: "Yes." He said: "When one of you stands for prayer, let him not wipe away the pebbles."