(31) باب النَّهْىِ عَنْ أَنْ يَتَنَخَّمَ الرَّجُلُ فِي قِبْلَةِ الْمَسْجِدِ
It was narrated from Ibn 'Umar that the Messenger of Allah (ﷺ) saw some sputum on the Qiblah wall. He scrapped it off then he turned to the people and said:
"When any one of you is praying, let him not spit in front of him, for Allah is in front of him when he prays."
Reference: Sunan an-Nasa'i 724
In-book reference: Book 8, Hadith 37
English translation: Vol. 1, Book 8, Hadith 725