It is narrated from Sayyiduna Hudhayfah (may Allah be pleased with him) that he passed by a man who was not completing his bowing and prostration. He (may Allah be pleased with him) said to him: How long have you been praying this kind of prayer? He said: I have been praying like this for forty years, or he said: for such and such a period. Sayyiduna Hudhayfah (may Allah be pleased with him) said: Then you have not prayed a single prayer for Allah in all that time. Mahdi says: I think he also said to him: If you were to die, you would die on other than the way of the Messenger of Allah (peace and blessings be upon him).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2726