Sunan an-Nasa'i
Book 8: The Book of the Masjids
كتاب المساجد
54 hadith in this book
Chapter 31 The Prohibition Of A Man Spitting Toward The Qiblah In The Masjid
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."
أَخْبَرَنَا قُتَيْبَةُ، عَنْ مَالِكٍ، عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم رَأَى بُصَاقًا فِي جِدَارِ الْقِبْلَةِ فَحَكَّهُ ثُمَّ أَقْبَلَ عَلَى النَّاسِ فَقَالَ " إِذَا كَانَ أَحَدُكُمْ يُصَلِّي فَلاَ يَبْصُقَنَّ قِبَلَ وَجْهِهِ فَإِنَّ اللَّهَ عَزَّ وَجَلَّ قِبَلَ وَجْهِهِ إِذَا صَلَّى " .
Hadith text, translations and grading are courtesy of Sunnah.com.