This was narrated by Abu Humayd, the Companion (may Allah be pleased with him), from the Prophet (peace and blessings of Allah be upon him).

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."