Narrated Abu Dhar (RA):

Allah's Messenger (ﷺ) said: "When one of you is praying he must not remove pebbles (from his face) for the mercy is facing him." [Reported by al-Khamsah with a Sahih (authentic) chain].

وَعَنْ أَبِي ذَرٍّ ‏- رضى الله عنه ‏- [1]‏ قَالَ : قَالَ رَسُولُ اَللَّهِ ‏- صلى الله عليه وسلم ‏-{ إِذَا قَامَ أَحَدُكُمْ فِي اَلصَّلَاةِ فَلَا يَمْسَحِ اَلْحَصَى , فَإِنَّ اَلرَّحْمَةَ تُوَاجِهُهُ } رَوَاهُ اَلْخَمْسَةُ بِإِسْنَادٍ صَحِيحٍ [2]‏