Sahih al-Bukhari 774
In-book no 774حَدَّثَنَا حَفْصُ بْنُ عُمَرَ، قَالَ حَدَّثَنَا شُعْبَةُ، عَنْ سُلَيْمَانَ، قَالَ سَمِعْتُ زَيْدَ بْنَ وَهْبٍ، قَالَ رَأَى حُذَيْفَةُ رَجُلاً لاَ يُتِمُّ الرُّكُوعَ وَالسُّجُودَ قَالَ مَا صَلَّيْتَ، وَلَوْ مُتَّ مُتَّ عَلَى غَيْرِ الْفِطْرَةِ الَّتِي فَطَرَ اللَّهُ مُحَمَّدًا صلى الله عليه وسلم.
Narrated Zaid bin Wahb: Hudhaifa saw a person who was not performing the bowing and prostration perfectly. He said to him, "You have not prayed and if you should die you would die on a religion other than that of Muhammad."