أَخْبَرَنَا قُتَيْبَةُ، قَالَ حَدَّثَنَا أَبُو عَوَانَةَ، عَنْ قَتَادَةَ، عَنْ أَنَسٍ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " الْبُصَاقُ فِي الْمَسْجِدِ خَطِيئَةٌ وَكَفَّارَتُهَا دَفْنُهَا " .
It was narrated that Anas said: "The Messenger of Allah (PBUH) said: 'Spitting in the Masjid is a sin, and its expiation is to bury it.'" Translation Not Available
Book Ref: Sunan An Nisai Book 8 Hadith 723
Web Ref: Sunan An Nisai Vol 1 Book 8 Hadith 724