Ubayy bin Kaab reported,

I was in the mosque when a man entered and began to pray, reciting in a manner I found objectionable. Then another man entered and recited differently from his companion. When we had finished the prayer, we all went together to the Messenger of Allah ﷺ.I said, "This man recited in a way I found objectionable, then another entered and recited differently from his companion."The Messenger of Allah ﷺ instructed them both to recite, and the Prophet ﷺ approved of how each of them recited. At that, a sense of denial fell into my heart such as I had not felt even in the days of ignorance.When the Messenger of Allah ﷺ saw what had overcome me, he struck my chest, and I broke out in a sweat, as though I were looking at Allah عز وجل in awe.He said to me, "Ubayy, word was sent to me to recite the Quran in one mode. I replied, asking that it be made easier for my community. It was sent to me a second time, to recite it in two modes. Again I replied, asking that it be made easier for my community. It was sent to me a third time, to recite it in seven modes, and for each reply you may ask of me a request."I said, "O Allah, forgive my community. O Allah, forgive my community." And I postponed the third request for the day when all of creation will turn to me in need, even Ibrahim ﷺ.

Muslim 1904

Sahih

حدثنا محمد بن عبد الله بن نمير حدثنا أبي حدثنا إسمعيل بن أبي خالد عن عبد الله بن عيسى بن عبد الرحمن بن أبي ليلى عن جده

عن أبي بن كعب قال

كنت في المسجد فدخل رجل يصلي فقرأ قراءة أنكرتها عليه ثم دخل آخر فقرأ قراءة سوى قراءة صاحبه فلما قضينا الصلاة دخلنا جميعا على رسول الله ﷺ فقلت إن هذا قرأ قراءة أنكرتها عليه ودخل آخر فقرأ سوى قراءة صاحبه فأمرهما رسول الله ﷺ فقرأا فحسن النبي ﷺ شأنهما فسقط في نفسي من التكذيب ولا إذ كنت في الجاهلية فلما رأى رسول الله ﷺ ما قد غشيني ضرب في صدري ففضت عرقا وكأنما أنظر إلى الله عز وجل فرقا فقال لي يا أبي أرسل إلي أن اقرأ القرآن على حرف فرددت إليه أن هون على أمتي فرد إلي الثانية اقرأه على حرفين فرددت إليه أن هون على أمتي فرد إلي الثالثة اقرأه على سبعة أحرف فلك بكل ردة رددتكها مسألة تسألنيها فقلت اللهم اغفر لأمتي اللهم اغفر لأمتي وأخرت الثالثة ليوم يرغب إلي الخلق كلهم حتى إبراهيم ﷺ

مسلم 1904صحيح
Contents
Reference
Commentary
Ayat
Collection
Sahih Muslim
Book
Virtues of the Quran and what relates to it
Chapter
Clarification that the Quran was revealed in seven modes and clarification of its meaning
Numbering
Darussalam 1904
Muslim 1904