It was narrated that Abu Hurairah said:The Messenger of Allah (ﷺ) said: “Whoever smoothes the pebbles, then he has engaged in Laghw.”**Meaning he has done what is not suitable.
حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا أَبُو مُعَاوِيَةَ، عَنِ الأَعْمَشِ، عَنْ أَبِي صَالِحٍ، عَنْ أَبِي هُرَيْرَةَ، قَالَ قَالَ رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ " مَنْ مَسَّ الْحَصَى فَقَدْ لَغَا " .
IbnMaja
Establishing the Prayer and the Sunnah Regarding Them • Hadith 1025