Sunan an-Nasa'i 726
سنن النسائي#726SahihIt was narrated that Tariq bin 'Abdullah Al-Muharibi said:'When you are praying, do not spit to the front or to your right. Spit behind you or to your left if there is no one there, otherwise do this.' And he spat beneath his foot and rubbed it
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 ZaiIsnaad Sahih
In-book reference: 8:39