Sahih al-Bukhari 808
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 (ﷺ) Muhammad."
حَدَّثَنَا الصَّلْتُ بْنُ مُحَمَّدٍ، قَالَ حَدَّثَنَا مَهْدِيٌّ، عَنْ وَاصِلٍ، عَنْ أَبِي وَائِلٍ، عَنْ حُذَيْفَةَ، رَأَى رَجُلاً لاَ يُتِمُّ رُكُوعَهُ وَلاَ سُجُودَهُ، فَلَمَّا قَضَى صَلاَتَهُ قَالَ لَهُ حُذَيْفَةُ مَا صَلَّيْتَ ـ قَالَ وَأَحْسِبُهُ قَالَ ـ وَلَوْ مُتَّ مُتَّ عَلَى غَيْرِ سُنَّةِ مُحَمَّدٍ صلى الله عليه وسلم‏.‏