“The Messenger of Allah ﷺ said: ‘When anyone of you gets up to perform prayer, then indeed mercy is facing him, so he should not smooth the pebbles.’” (Using translation from Ibn Mājah 1027)
النَّبِيَّ ﷺ إِذَا قَامَ أَحَدُكُمْ إِلَى الصَّلَاةِ فَإِنَّ الرَّحْمَةَ تُوَاجِهُهُ فَلَا يَمْسَحِ الْحَصَى