Zayd b. Wahb reports:
We were once sitting in the masjid with Ḥudhayfah (ibn Al-Yamān) – Allah be pleased with him, when a man entered from the gates of Kindah and stood to pray; but he did not complete the bowing or prostration postures. When he had finished praying, Ḥudhayfah asked him, “How long have you been praying in this manner?” The man replied, “For forty years.” Ḥudhayfah said, “You have not prayed for forty years! And if you were to die praying in this manner you would die upon a way (fiṭrah) other than the way of Muḥammad – Allah’s peace and blessings be upon him.”
Al-Bukhārī, Al-Ṣaḥīḥ, The Book of Adhān, without the mention of 40 years. A version in Al-Nasā`ī, Chapter on the Deficient Prayer, mentions the question and reply about 40 years. Shaykh Al-Albānī graded its chain of transmission ṣaḥīḥ in Sahīh Sunan Al-Nasā`ī no. 1311.