Muhammed bin Mansoor (rahimahullah) narrates the following incident:

On one occasion, while we were in the musjid, seated in the gathering of Imaam Bukhaari (rahimahullah), a certain person in the musjid removed some dirt from his beard and threw it on the ground. I looked towards Imaam Bukhaari (rahimahullah) to see whether he had noticed what the person had done. I observed that Imaam Bukhaari (rahimahullah) looked at the dirt on the floor and thereafter shifted his gaze towards the students in the gathering.