Mishkat al-Masabih 4 Prayer كتاب الصلاة 402

وَعَنْ مُعَيْقِيبٍ عَنِ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ فِي الرَّجُلِ يُسَوِّي التُّرَابَ حَيْثُ يَسْجُدُ؟ قَالَ: «إِنْ كُنْتَ فَاعِلًا فَوَاحِدَةً»

Mu’aiqib quoted the Prohpet as saying about a man who smoothed the ground where he prostrated himself, “If you do it, do it only once.” (Bukhari and Muslim.)