It is narrated from Sayyiduna Abu Dharr (may Allah be pleased with him) that the Noble Prophet (peace and blessings be upon him) said: When any of you stands for prayer, he should not clear the pebbles, nor move them, nor touch them, because mercy is before him.
Hadith Referenceالفتح الربانی / أبواب الأذ كار الواردة عقب الصلاة / 1899