Messenger of Allah ﷺ saw sputum on the wall of the mosque in the direction of the Qibla and scraped it off. He faced the people and said, "Whenever any one of you is praying, he should not spit in front of him because in the prayer Allah is in front of him." (Using translation from Bukhārī 406)  

أَنَّ رَسُولَ اللهِ ﷺ رَأَى بُصَاقًا فِي جِدَارِ الْقِبْلَةِ فَحَكَّهُ ثُمَّ أَقْبَلَ عَلَى النَّاسِ فَقَالَ «إِذَا كَانَ أَحَدُكُمْ يُصَلِّي فَلَا يَبْزُقْ قِبَلَ وَجْهِهِ فَإِنَّ اللهَ قِبَلَ وَجْهِهِ إِذَا صَلَّى»