Al-Bukhaari, may Allah have mercy on him, reported from Mu’ayqeeb, may Allah be pleased with him, that the Prophet, peace and blessings of Allah be upon him, said concerning a man’s smoothing the ground when he prostrates:
“If you have to do that, then do it only once.” (Fath al-Baari, 3/79).
The Messenger of Allah, peace and blessings of Allah be upon him, said:
“Do not wipe (the ground) when you are praying, but if you have to, then do it only once.” (Reported by Abu Dawood, no. 946)
The reason for this prohibition is so as to maintain khushu, and so that a person will not make too many extra movements in prayer. If the place where one is going to prostrate needs to be smoothed, it is better to do this before starting to pray.
This also applies to wiping the forehead or nose when praying. The Prophet, peace and blessings of Allah be upon him, used to prostrate in water and mud, which would leave traces on his forehead, but he did not bother to wipe it off every time he raised his head from sujud. It remained there because he was so deeply absorbed in his prayer and his khushu was so strong that he took not notice of it.
The Prophet, peace and blessings of Allah be upon him, said:
“Prayer is an occupation in itself.” (Reported by al-Bukhaari, Fath al-Baari, 3/72).
Ibn Abi Shaybah reported that Abu’l-Darda’ said: “Even if I were to get red camels, I would not like to wipe the gravel from my forehead.” ‘Ayaad said: “The salaf did not like to wipe their foreheads before they finished praying.” (al-Fath, 3/79).