Umar ibn al-Khattab said, "I heard Hisham ibn Hakim ibn Hizam reciting Surat al-Furqan (Sura 25) differently from me, and it was the Messenger of Allah, may Allah bless him and grant him peace, who had recited it to me. I was about to rush up to him but I granted him a respite until he had finished his prayer. Then I grabbed him by his cloak and took him to the Messenger of Allah, may Allah bless him and grant him peace, and said, 'Messenger of Allah, I heard this man reciting Surat al-Furqan differently from the way you recited it to me.' The Messenger of Allah, may Allah bless him and grant him peace, said, 'Let him go.' Then he said, 'Recite, Hisham,' and Hisham recited as I had heard him recite. The Messenger of Allah, may Allah bless him and grant him peace, said, 'It was sent down like that.' Then he said to me, 'Recite' and I recited the sura, and he said, 'It was sent down like that. This Qur'an was sent down in seven (different) ways [of qirat], so recite from it whatever is easy for you'.

Malik :: Book 15 : Hadith 15.4.5