The Book of Forgetfulness (In Prayer)
13/7. Chapter:
The prohibition of smoothing the pebbles while praying
Sunan an-Nasai
أَخْبَرَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، وَالْحُسَيْنُ بْنُ حُرَيْثٍ، - وَاللَّفْظُ لَهُ - عَنْ سُفْيَانَ، عَنِ الزُّهْرِيِّ، عَنْ أَبِي الأَحْوَصِ، عَنْ أَبِي ذَرٍّ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " إِذَا قَامَ أَحَدُكُمْ فِي الصَّلاَةِ فَلاَ يَمْسَحِ الْحَصَى فَإِنَّ الرَّحْمَةَ تُوَاجِهُهُ " .
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 1191In-book reference : Book 13, Hadith 13English translation : Vol. 2, Book 13, Hadith 1192