Sunan an-Nasa'i 724
سنن النسائي#724SahihIt 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
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Abu GhuddahSahih
Al-AlbaniSahih
Zubair Ali ZaiSahih - Agreed Upon
In-book reference: 8:37