Sahih al-Bukhari, Book 8, Hadith 58 (In-Book) ⓘ

Narrated `Abdullah bin `Umar: Allah's Messenger 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."

حَدَّثَنَا عَبْدُ اللَّهِ بْنُ يُوسُفَ، قَالَ أَخْبَرَنَا مَالِكٌ، عَنْ نَافِعٍ، عَنْ عَبْدِ اللَّهِ بْنِ عُمَرَ،‏.‏ أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم رَأَى بُصَاقًا فِي جِدَارِ الْقِبْلَةِ فَحَكَّهُ، ثُمَّ أَقْبَلَ عَلَى النَّاسِ فَقَالَ ‏ "‏ إِذَا كَانَ أَحَدُكُمْ يُصَلِّي، فَلاَ يَبْصُقْ قِبَلَ وَجْهِهِ، فَإِنَّ اللَّهَ قِبَلَ وَجْهِهِ إِذَا صَلَّى ‏" ‏‏.‏