(13) باب النَّهْىِ عَنِ الْبُصَاقِ، فِي الْمَسْجِدِ فِي الصَّلاَةِ وَغَيْرِهَا
Abdullah b. Umar reported:
The Messenger of Allah (ﷺ) saw spittle on the wall towards Qibla, and scratched it away and then turning to the people said: When any one of you prays, he must not spit in front of him, for Allah is in front of him when he is engaged in prayer.
Reference: Sahih Muslim 547 a
In-book reference: Book 5, Hadith 61
USC-MSA web (English) reference(deprecated numbering scheme): Book 4, Hadith 1116