Sahih Al Bukhari Hadith Number 1207

Narrated Mu’aiqib: The Prophet (peace be upon him) talked about a man leveling the earth on prostrating, and said, “If you have to do so, then do it once.”

21  Actions while Praying
Hadith number 1207
Volume no 2
Chapter: 8 (The levelling of small stones during As-Salat)