(4) Prayer
كتاب الصلاة
(20b) Chapter: What may not be done during Prayer and what is permitted - Section 2
(19) بَابُ مَا لَا يَجُوزُ مِنَ الْعَمَلِ فِي الصَّلَاةِ وَمَا يُبَاحُ مِنْهُ - الفصل الثاني
Mishkat al-Masabih 1001 
Abu Dharr reported God’s Messenger as saying, “When one of you gets up to pray he must not remove pebbles, for mercy is facing him.”* * Meaning that such an action is unfitting when one is in God’s presence. Ahmad, Tirmidhi, Abu Dawud, Nasa’i and Ibn Majah transmitted it.
وَعَنْ أَبِي ذَرٍّ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «إِذَا قَامَ أَحَدُكُمْ إِلَى الصَّلَاةِ فَلَا يَمْسَحِ الْحَصَى فَإِنَّ الرَّحْمَةَ تُوَاجِهُهُ» . رَوَاهُ أَحَمَدُ وَالتِّرْمِذِيُّ وَأَبُو دَاوُدَ وَالنَّسَائِيُّ وَابْنُ مَاجَه
 ضَعِيف  (الألباني)حكم :
Reference : Mishkat al-Masabih 1001
In-book reference : Book 4, Hadith 421