(a) It is narrated from Abu Ja'far al-Qari: I saw Sayyiduna Abdullah bin Umar (may Allah be pleased with them both); when he bent down to prostrate, he would make a slight movement to remove the pebbles from the place of his prostration.
(b) Imam al-Bayhaqi (may Allah have mercy on him) says: This much is permitted, and where the word of dislike (karahah) is used, what is meant is that one should not play with them needlessly. If he levels them before the prayer, as is established from the practice of Sayyiduna Uthman (may Allah be pleased with him), that is much better. Wa billahi al-tawfiq (and success is from Allah alone).
(c) It has been narrated to us from Sa'id bin al-Musayyib (may Allah have mercy on him) that he saw a man playing with the pebbles (during prayer) and said: If there were humility in his heart, his other limbs would also be humble.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3550