Sahih Muslim 552
Sahih Muslim · Book 5: The Book of Mosques and Places of Prayer · 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
Shu'ba reported:
حَدَّثَنَا يَحْيَى بْنُ حَبِيبٍ الْحَارِثِيُّ ، حَدَّثَنَا خَالِدٌ، - يَعْنِي ابْنَ الْحَارِثِ - حَدَّثَنَا شُعْبَةُ ، قَالَ سَأَلْتُ قَتَادَةَ عَنِ التَّفْلِ، فِي الْمَسْجِدِ فَقَالَ سَمِعْتُ أَنَسَ بْنَ مَالِكٍ ، يَقُولُ سَمِعْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يَقُولُ " التَّفْلُ فِي الْمَسْجِدِ خَطِيئَةٌ وَكَفَّارَتُهَا دَفْنُهَا " .
I asked Qatada about spitting, in the mosque. He said: I heard Anas b. Malik say: I heard the Messenger of Allah (ﷺ) say: Spitting in the mosque is a sin, and its expiation is that it should be buried.