Jami at-Tirmidhi 572
Jami at-Tirmidhi · Book 6: The Book on Traveling · (What Has Been Related) About It Being Disliked To Spit In The Masjid
Anas bin Malik narrated that :
حَدَّثَنَا قُتَيْبَةُ ، حَدَّثَنَا أَبُو عَوَانَةَ ، عَنْ قَتَادَةَ ، عَنْ أَنَسِ بْنِ مَالِكٍ ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " الْبُزَاقُ فِي الْمَسْجِدِ خَطِيئَةٌ وَكَفَّارَتُهَا دَفْنُهَا " . قَالَ أَبُو عِيسَى وَهَذَا حَدِيثٌ حَسَنٌ صَحِيحٌ .
the Messenger of Allah said: "To spit in the Masjid is a sin, and burying it is its atonement."
Grade: Sahih (Darussalam)