Language:
كتاب الأدب
78  
Good Manners and Form (Al-Adab)
(75)
Chapter: What to say when one is angry or harsh for Allah's sake
(75)
بَابُ مَا يَجُوزُ مِنَ الْغَضَبِ وَالشِّدَّةِ لأَمْرِ اللَّهِ
Sahih al-Bukhari 6111

Narrated `Abdullah bin `Umar:

While the Prophet (ﷺ) was praying, he saw sputum (on the wall) of the mosque, in the direction of the Qibla, and so he scraped it off with his hand, and the sign of disgust (was apparent from his face) and then said, "Whenever anyone of you is in prayer, he should not spit in front of him (in prayer) because Allah is in front of him."

حَدَّثَنَا مُوسَى بْنُ إِسْمَاعِيلَ، حَدَّثَنَا جُوَيْرِيَةُ، عَنْ نَافِعٍ، عَنْ عَبْدِ اللَّهِ ـ رضى الله عنه ـ قَالَ بَيْنَا النَّبِيُّ صلى الله عليه وسلم يُصَلِّي رَأَى فِي قِبْلَةِ الْمَسْجِدِ نُخَامَةً، فَحَكَّهَا بِيَدِهِ، فَتَغَيَّظَ ثُمَّ قَالَ ‏ "‏ إِنَّ أَحَدَكُمْ إِذَا كَانَ فِي الصَّلاَةِ فَإِنَّ اللَّهَ حِيَالَ وَجْهِهِ، فَلاَ يَتَنَخَّمَنَّ حِيَالَ وَجْهِهِ فِي الصَّلاَةِ ‏"‏‏.‏
Reference : Sahih al-Bukhari 6111
In-book reference : Book 78, Hadith 138
USC-MSA web (English) reference : Vol. 8, Book 73, Hadith 132
  (deprecated numbering scheme)