In the early days of his Prophethood, when the Holy Prophet (SAWS) received the verses of the Holy Quran revealed to him, he used to recite the same simultaneously, lest he should forget them. It was a strenuous exercise for him, because he felt it was much too difficult to listen to the revelation, to understand it correctly, and to learn it by heart, all at the same time. Allah Almighty relieved him from this burden when He revealed the following verses of the Holy Quran:
“Move not your tongue with it in order to hasten it. It is on Us to gather it (in your heart) and to recite it. So, when We read it, follow its reading. Then it is on Us to explain it.” (75:16,19)
In the last sentence, Allah Almighty has promised the Holy Prophet (SAWS) to explain the verses of the Holy Quran to him. It is evident that this explanation is something separate from the Holy Quran itself. It is not the Holy Quran. It is its explanation or its exegesis.
Therefore, it should necessarily be in some other form, distinct from the words of the Holy Book. And this is exactly what is meant by the ‘unrecited revelation’. But the two kinds of revelation, though different in their form,
are both revealed to the Holy Prophet (SAWS) both are from Allah, and both are to be believed and obeyed by the Muslims.