Sahih Bukhari Volume 4, Book 60, Hadith 3477

حَدَّثَنَا آدَمُ، حَدَّثَنَا شُعْبَةُ، حَدَّثَنَا عَبْدُ الْمَلِكِ بْنُ مَيْسَرَةَ، قَالَ سَمِعْتُ النَّزَّالَ بْنَ سَبْرَةَ الْهِلاَلِيَّ، عَنِ ابْنِ مَسْعُودٍ ـ رضى الله عنه ـ قَالَ سَمِعْتُ رَجُلاً، قَرَأَ، وَسَمِعْتُ النَّبِيَّ صلى الله عليه وسلم يَقْرَأُ خِلاَفَهَا فَجِئْتُ بِهِ النَّبِيَّ صلى الله عليه وسلم فَأَخْبَرْتُهُ فَعَرَفْتُ فِي وَجْهِهِ الْكَرَاهِيَةَ وَقَالَ ‏"‏ كِلاَكُمَا مُحْسِنٌ، وَلاَ تَخْتَلِفُوا، فَإِنَّ مَنْ كَانَ قَبْلَكُمُ اخْتَلَفُوا فَهَلَكُوا ‏"‏‏

Narrated By Ibn Mas'ud : I heard a person reciting a (Qur'anic) Verse in a certain way, and I had heard the Prophet reciting the same Verse in a different way. So I took him to the Prophet and informed him of that but I noticed the sign of disapproval on his face, and then he said, "Both of you are correct, so don't differ, for the nations before you differed, so they were destroyed."