Read Surah Al-Bayyina

أن سبب تخصيصه بذلك أنه وجد اثنين من الصحابة رضي الله عنهم قد...

The reason for his specification with this is that he found two of the Companions, may God be pleased with them, had disagreed with him in recitation, so he took them to the Prophet, may God's peace and blessings be upon him, who ordered them to recite, and they recited to him, and he was pleased with them. He said: So, the denial that was in my heart fell away, more than it was in the pre-Islamic era. The Prophet, may God's peace and blessings be upon him, struck my chest, and I sweated, and it was as if I saw God, the Most Exalted, in a vision. Then, he told me the story of the revelation in seven dialects. The surah in which the disagreement occurred was {An-Nahl}, which includes that God will send His Messenger, may God's peace and blessings be upon him, on the Day of Resurrection as a witness, and that the Book was revealed to him as an explanation of everything, and as guidance and mercy. It also includes that the Holy Spirit was revealed to him with the truth to strengthen those who believe, and that the Jews disagreed about the Sabbath. The surah {Kun} is, in its brevity, a summary of all that is in {An-Nahl} in its length, with an increase. It includes a warning against doubt after clarification, and the repugnance of the state of one who does that, and that his state will be like that of the disbelievers among the People of the Book in stubbornness, and will be the worst of creatures. So, the Prophet, may God's peace and blessings be upon him, recited it to him, may God be pleased with him, as a reminder to him of all that, in the most eloquent and concise manner, so that it would be the quickest for him to imagine, and would be the most firmly established in the soul, and the most firmly rooted in the heart, and the most beloved to nature. So, God specified him with firmness, and wanted for him stability, and he was one of those who were desired for what his heart had reached, by the blessing of the Prophet's, may God's peace and blessings be upon him, strike on his chest, from the removal of veils, and the repulsion of devils, and the vision of the splendors of the Holy.