Surah al-A`la (The Most High ) 87 : 16

The subject matter shows that this too is one of the earliest Surahs to be revealed, and the words: “We shall enable you to recite, then you shall never forget” of verse 6 also indicate that it was sent down in the period when the Messenger was not yet fully accustomed to receiving Revelation and at the time Revelation came down he feared lest he should forget its words. If this verse is read along with verse 114 of Surah 20: Ta Ha and verses 16-19 of Surah 75: al-Qiyamah (The Resurrection) and the three verses are also considered with regard to their styles and contexts, the sequence of events seems to be that first in this Surah the Prophet was reassured to the effect: “Do not at all worry: We shall enable you to recite this Word, then you shall not forget it.” Then after a lapse of time, on another occasion, when Surah 75: al-Qiyamah was being revealed, the Prophet involuntarily began to rehearse the words of the Revelation. Thereupon it was said: “O Prophet do not move your tongue to remember this Revelation hastily. It is for Us to have it remembered and read. Therefore when We are reciting it, listen to its recital carefully. Again, it is for Us to explain its meaning.” Last of all, on the occasion of the revelation of Surah 20: Ta Ha, the Prophet on account of human weakness, again became afraid lest his memory should fail to preserve some portion of the 113 verses which were continuously revealed at that time, and therefore, he began to memorise them. Thereupon, it was said: “And see that you do not hasten to recite the Qur’an before its revelation is completed to you.” After this, it never so happened that he felt any such danger, for apart from these three places, there is no other place in the Qur’an where there might be a reference to this matter.