When Rasulullah (sallallahu ‘alaihi wasallam) reached forty and entered the cave of Hira, as per his blessed habit, an angel suddenly entered the cave and greeted him with salaam. The angel then said, “Read!” Rasulullah (sallallahu ‘alaihi wasallam) replied, “I am unable to read.” Rasulullah (sallallahu ‘alaihi wasallam) recounts, “Upon this, the angel embraced me so forcefully that there was no limit to my difficulty. He then released me saying, “Read!” Yet again, I responded:
ما أنا بقارئ
“I am unable to read.”
Continuing further, Rasulullah (sallallahu ‘alaihi wasallam) relates, “The angel likewise forcefully embraced me a second and then a third time, thereafter releasing me and instructing me to recite the following verses:
اقرَأ بِاسمِ رَبِّكَ الَّذى خَلَقَ ﴿١﴾ خَلَقَ الإِنسـٰنَ مِن عَلَقٍ ﴿٢﴾ اقرَأ وَرَبُّكَ الأَكرَمُ ﴿٣﴾ الَّذى عَلَّمَ بِالقَلَمِ ﴿٤﴾ عَلَّمَ الإِنسـٰنَ ما لَم يَعلَم ﴿٥﴾
“Read (with the aid) of the name of your Rabb Who has created (the entire universe). He has created (above all) man from a clot of blood. Read! And your Rabb is the most gracious Who has taught (knowledge) by the use of the pen. He has taught man that which he did not know.” [Surah ‘Alaq v. 1]
(Extracted from Seeratul Mustafa 1/133-135)