It wasnarrated that Abu Dharr said:
"The Messenger of Allah (ﷺ)said:'When anyone of you gets up to perform prayer, then indeed mercyisfacing him, so he should not smooth the pebbles.'" (JA)
English reference (JA): Vol. 1, Book 5, Hadith 1027 (JA)
Arabic reference (JA): Book 5, Hadith 1080 (JA)