Sunan an-Nasa'i
Book 8: The Book of the Masjids
كتاب المساجد
54 hadith in this book
Chapter 30 Spitting In The Masjid
باب الْبُصَاقِ فِي الْمَسْجِدِ
It was narrated that Anas said: "The Messenger of Allah (ﷺ) said: 'Spitting in the Masjid is a sin, and its expiation is to bury it.'"
أَخْبَرَنَا قُتَيْبَةُ، قَالَ حَدَّثَنَا أَبُو عَوَانَةَ، عَنْ قَتَادَةَ، عَنْ أَنَسٍ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " الْبُصَاقُ فِي الْمَسْجِدِ خَطِيئَةٌ وَكَفَّارَتُهَا دَفْنُهَا " .
Hadith text, translations and grading are courtesy of Sunnah.com.