Hadith 1425
Sayyiduna Mu'ayqib ibn Abi Talhah (may Allah be pleased with him) narrated that the Messenger of Allah (peace and blessings be upon him) was asked about removing pebbles in the mosque, so he (peace be upon him) said: "If it is extremely necessary, then only once." Hisham said: I think what was meant is that one should remove the pebbles only once.
Hadith 1426
Sayyiduna Abu Dharr (may Allah be pleased with him) said: The Messenger of Allah (peace and blessings be upon him) said: "When any one of you stands for prayer, the mercy of Allah is before him, so he should not remove pebbles."