Narrated Abu Wail:Hudhaifa said, "I saw a person not performing his bowing and prostrations perfectly. When he completed the prayer, I told him that he had not prayed." I think that Hudhaifa added (i.e. said to the man), "Had you died, you would have died on a tradition other than that of the Prophet Muhammad (ﷺ)

English translation · Sahih al-Bukhari