Sahih al-Bukhari 3476
Narrated Ibn Mas`ud:
I heard a person reciting a (Qur'anic) Verse in a certain way, and I had heard the Prophet (ﷺ) reciting the 
same Verse in a different way. So I took him to the Prophet (ﷺ) 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."
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 ‏"‏‏.‏