The Messenger of Allah ﷺ said, "Spitting in the mosque is a sin, and its expiation is to bury it."
حدثنا الضحاك بن مخلد حدثنا سعيد بن أبي عروبة عن قتادة
أن رسول الله ﷺ قال النخاعة في المسجد خطيئة وكفارتها دفنها
Its isnad is sahih, it was previously mentioned at 12825 and 12826.