The Book of Mosques and Places of Prayer
5/13. 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
Sahih Muslim
وَحَدَّثَنَا يَحْيَى بْنُ يَحْيَى، وَقُتَيْبَةُ بْنُ سَعِيدٍ، قَالَ يَحْيَى أَخْبَرَنَا وَقَالَ، قُتَيْبَةُ حَدَّثَنَا أَبُو عَوَانَةَ، عَنْ قَتَادَةَ، عَنْ أَنَسِ بْنِ مَالِكٍ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " الْبُزَاقُ فِي الْمَسْجِدِ خَطِيئَةٌ وَكَفَّارَتُهَا دَفْنُهَا " .
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.
Reference : Sahih Muslim 552aIn-book reference : Book 5, Hadith 69USC-MSA web (English) reference : Book 4, Hadith 1124