Abdullah bin Masud reported,

The Messenger of Allah ﷺ taught me to recite Surah Ha-Mim, meaning al-Ahqaf. One evening I went to the mosque, and a small group sat with me. I said to one of them, "Recite to me." He began reciting words I had not learned that way.I asked him, "Who taught you this recitation?"He replied, "The Messenger of Allah ﷺ taught me."So we went together to the Messenger of Allah ﷺ, and there was already a man with him. I said, "We have differed in our recitation."The face of the Messenger of Allah ﷺ changed, and he was distressed when I mentioned the disagreement. He said, "Those before you were destroyed only by disagreement."Then he whispered something to Ali, and Ali said, "The Messenger of Allah ﷺ commands you that each man among you should recite as he was taught."So we departed, and each one of us was reciting words that his companion did not recite the same way.

عن عبد الله بن مسعود قال

أقرأني رسول الله ﷺ سورة حم- يعني الأحقاف، ورحت إلى المسجد عشية، فجلس إلي رهط، فقلت لرجل من الرهط: اقرأ على، فإذا هو يقرأ حروفا، لا أقرأها، فقلت له: من أقرأكها؟ قال: أقرأني رسول الله ﷺ. فانطلقنا إلى رسول الله ﷺ، وإذا عنده رجل، فقلت له: اختلفنا في قراءتنا، فإذا وجه رسول الله ﷺ قد تغير، ووجد في نفسه حين ذكرت له الاختلاف، فقال: إنما أهلك من قبلكم الاختلاف ثم أسر إلى علي فقال علي: إن رسول الله ﷺ يأمركم: أن يقرأ كل رجل منكم كما علم، فانطلقنا، وكل رجل منا يقرأ حروفا لا يقرؤها صاحبه.