حَدَّثَنَا مُسَدَّدٌ، حَدَّثَنَا أَبُو عَوَانَةَ، عَنْ قَتَادَةَ، عَنْ أَنَسِ بْنِ مَالِكٍ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏"‏ الْبُزَاقُ فِي الْمَسْجِدِ خَطِيئَةٌ وَكَفَّارَتُهَا دَفْنُهَا ‏"‏ ‏.‏

Anas reported: The Messenger of Allah (PBUH) said: Spitting in the mosque is a sin and it is expiated by burying the spittle. Translation Not Available

Book Ref: Sunan Abi Dawud Book 2 Hadith 475
Web Ref:  Sunan Abi Dawud Book 2 Hadith 475