It is narrated from Hazrat Abu Dharr (may Allah be pleased with him) that I asked the Noble Prophet (peace and blessings be upon him) about everything, even about removing pebbles during prayer. The Noble Prophet (peace and blessings be upon him) replied: "Level it only once, or leave it (as it is)."
Hadith Referenceمسند احمد / مسند الأنصار رضي الله عنهم / 21446
Hadith Gradingحکم دارالسلام:حديث صحيح، وهذا الإسناد ضعيف، مؤمل وابن أبى ليلي ضعيفان، لكنهما متابعان