(13) Chapter: The prohibition of spitting in the masjid, during prayer and at other times. The prohibition of a praying person spitting in front of him or to his right
باب النَّهْىِ عَنِ الْبُصَاقِ، فِي الْمَسْجِدِ فِي الصَّلاَةِ وَغَيْرِهَا
Anas b. Malik reported:
The Messenger of Allah (ﷺ) said: Spitting in a mosque is a sin, and its expiation is that it should be buried.