He saw a man who was not completing his bowing and prostration properly, so he said, "You have not prayed. If you were to die, you would die upon other than the natural way upon which Allah created Muhammad ﷺ."In another narration, "You would die upon other than the way of Muhammad ﷺ."
أنه رأى رجلا لا يتم الركوع والسجود قال: ما صليت، ولو مت مت على غير الفطرة التي فطر الله محمدا ﷺ. وفي رواية: مت على غير سنة محمد ﷺ.
Bukhari narrated it in the chapter on the adhan (791, 808) through both routes, from Huzaifa. Bukhari included this hadith in his Jami based on the view of the majority that when a companion says "the sunnah of Muhammad" or "his fitrah," it counts as a hadith attributed to the Prophet (marfu). Some scholars disagreed with this. Hafiz said, the more correct view is the first one.As for what Imam Ahmad narrated (23258) through the route of Amash, and Nasai (1312) through the route of Talha bin Musarrif, both from Zayd bin Wahb, who said, Huzaifa entered the masjid and saw a man praying near the doors of Kinda. The man was not completing his ruku or his sujud properly. When he finished, Huzaifa asked him, "How long have you been praying like this?" He said, "For forty years." Huzaifa said to him, "You have not prayed for forty years. If you were to die while praying like this, you would die outside the fitrah upon which Muhammad ﷺ was created."He said, then Huzaifa turned to teach him, and said, "A man may shorten his prayer, yet still complete the ruku and the sujud properly."Although its chain of transmission is sahih, it may be understood as an exaggeration, because Huzaifa died in the year thirty-six. On this basis, the beginning of this man's prayer would have been four years or more before the Hijrah, and perhaps the prayer had not yet been made obligatory at that time. So perhaps Huzaifa spoke in general terms, meaning it as an exaggeration. See Fath al-Bari (2/275).