Imam Ahmad : 21213

حَدَّثَنَا زَيْدُ بْنُ الْحُبَابِ أَخْبَرَنَا حُسَيْنُ بْنُ وَاقِدٍ حَدَّثَنَا أَبُو غَالِبٍ أَنَّهُ سَمِعَ أَبَا أُمَامَةَ يَقُولُ قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ التَّفْلُ فِي الْمَسْجِدِ سَيِّئَةٌ وَدَفْنُهُ حَسَنَةٌ

Narrated to us [Zaid bin Al Hubab] Narrated to us [Husain bin Waqid] Narrated to us [Abu Ghalib] that he heard [Abu Umamah] say: Rasulullah Peace be upon himsaid: "Spitting in the mosque is evil and harboring it is good.