Sahih al Bukhari 1207
Actions while Praying
حَدَّثَنَا أَبُو نُعَيْمٍ، حَدَّثَنَا شَيْبَانُ، عَنْ يَحْيَى، عَنْ أَبِي سَلَمَةَ، قَالَ حَدَّثَنِي مُعَيْقِيبٌ، أَنَّ النَّبِيَّ صلى الله عليه وسلم قَالَ فِي الرَّجُلِ يُسَوِّي التُّرَابَ حَيْثُ يَسْجُدُ قَالَ " إِنْ كُنْتَ فَاعِلاً فَوَاحِدَةً ".
Narrated Mu'aiqib:The Prophet (ﷺ) talked about a man leveling the earth on prostrating, and said, "If you have to do so, then do it once
Text from the public-domain hadith-api dataset. Numbering follows that dataset and can differ by a few from some printed editions — check the wording, not only the number.