(7) باب النَّهْىِ عَنْ مَسْحِ الْحَصَى، فِي الصَّلاَةِ
It was narrated that Abu Dharr said:
"The Messenger of Allah (ﷺ) said: 'When any one of you stands in prayer, let him not smooth the pebbles, for he is facing Mercy.'"
Reference: Sunan an-Nasa'i 1191
In-book reference: Book 13, Hadith 13
English translation: Vol. 2, Book 13, Hadith 1192