The Book of Mosques and Places of Prayer
5/13. Chapter:
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
Sahih Muslim
وَحَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، عَنْ مَالِكِ بْنِ أَنَسٍ، فِيمَا قُرِئَ عَلَيْهِ عَنْ هِشَامِ بْنِ عُرْوَةَ، عَنْ أَبِيهِ، عَنْ عَائِشَةَ، أَنَّ النَّبِيَّ صلى الله عليه وسلم رَأَى بُصَاقًا فِي جِدَارِ الْقِبْلَةِ أَوْ مُخَاطًا أَوْ نُخَامَةً فَحَكَّهُ .
'A'isha reported: The Apostle of Allah (may, peace be upon him) saw spittle or snot or sputum, sticking to the wall towards Qibla and scratched it off.
Reference : Sahih Muslim 549In-book reference : Book 5, Hadith 65USC-MSA web (English) reference : Book 4, Hadith 1120