Hadith 229

Sahih Bukhari

Book 10: Call to Prayers (Adhaan)

Chapter 151

No cleaning (rubbing) one's forehead and nose till one has completed As-Salat (the prayer)

باب مَنْ لَمْ يَمْسَحْ جَبْهَتَهُ وَأَنْفَهُ حَتَّى صَلَّى

And Abu 'Abdullah said: I saw Al-Humaidi quoting this Hadith (No.798) to support his argument that the forehead should not be cleaned (rubbed) in As-Salat (prayer). ​​
قالَ أَبُو عَبْدِ اللَّهِ : رَأَيْتُ الحُمَيْدِيَّ يَحْتَجُّ بِهٰذَا الحَدِيثِ أَنْ لَا يَمْسَحَ الجَبْهَةَ فِي الصَّلاةِ.
Sahih al-Bukhari 836
حَدَّثَنَا مُسْلِمُ بْنُ إِبْرَاهِيمَ، قَالَ حَدَّثَنَا هِشَامٌ، عَنْ يَحْيَى، عَنْ أَبِي سَلَمَةَ، قَالَ سَأَلْتُ أَبَا سَعِيدٍ الْخُدْرِيَّ فَقَالَ رَأَيْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يَسْجُدُ فِي الْمَاءِ وَالطِّينِ حَتَّى رَأَيْتُ أَثَرَ الطِّينِ فِي جَبْهَتِهِ‏.‏
Abu Sa`id Al-Khudri:

I saw Allah's Messenger (ﷺ) prostrating in mud and water and saw the mark of mud on his forehead.