Hadithcore
Hadith #500320

Yahya related to me from Malik from Abd ar-Rahman ibn al-Mujabbar that he used to see Salim ibn Abdullah pull the cloth away fiercely from the mouth of any man he saw covering his mouth while praying.

وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ عَبْدِ الرَّحْمَنِ بْنِ الْمُجَبَّرِ، أَنَّهُ كَانَ يَرَى سَالِمَ بْنَ عَبْدِ اللَّهِ إِذَا رَأَى الإِنْسَانَ يُغَطِّي فَاهُ وَهُوَ يُصَلِّي جَبَذَ الثَّوْبَ عَنْ فِيهِ جَبْذًا شَدِيدًا حَتَّى يَنْزِعَهُ عَنْ فِيهِ ‏.‏

References1 variant
Arabic/English book reference
Book 1, Hadith 31