Bukhari

Hadith Commentary:
The portion of the Noble Qur'an that was revealed before the Hijrah is called Makki, and that which was revealed after the Hijrah is called Madani. It is very important to remember this principle.

Hadith Commentary:
1.
The heading established by Imam Bukhari rahimahullah consists of two parts:
How did the revelation descend? What was revealed first? Whereas, at the beginning of Sahih Bukhari, he established a heading in these words:
(Bab kayfa kana bad’ al-wahy ila Rasulillah sallallahu alayhi wa sallam)
"How did the beginning of revelation to the Messenger of Allah sallallahu alayhi wa sallam occur?"
Regarding the difference between these two, Hafiz Ibn Hajar rahimahullah states that the term "descent" (nuzul) necessitates the existence of the being through whom the revelation was sent down, i.e., the Angel of Revelation.
And "revelation" (wahy) is general, whether it is in the form of sending down (inzal) or inspiration (ilham), whether the revelation occurs in a waking state or in the form of a dream.
(Fath al-Bari: 6/9)
2.
According to our inclination, it is considered in this heading: what was the manner of the descent of the Qur’an, which has been mentioned in the virtues of the Qur’an.
That is, the Qur’an was not sent down all at once, but rather gradually, as needed.
In this regard, the period of revelation is twenty-three (23) years, and the period of continuous revelation spans twenty (20) years, as mentioned in the above hadith.
The first three years are not included in this, because after the first revelation, the series of revelation was interrupted for about three years, which is called the Fatrah of Revelation (Fatrat al-Wahy).
Although the coming and going of the angel continued, the series of continuous revelation began after three years.
3.
From this hadith, it is understood that the Qur’an was completed over twenty years according to the principle of gradualness (tadreej), and this is a virtue of this blessed Book. Allah the Exalted says:
"The disbelievers say: Why was the entire Qur’an not sent down to him at once? (It is sent down gradually) so that We may strengthen your heart thereby, and We have recited it to you gradually, in stages. And whenever they bring you an argument, We bring you the truth and the best explanation." (: al-Furqan: 32-33)
In this verse, three benefits of the gradual revelation of the Qur’an are mentioned:
➊. In discouraging circumstances, the need to console and strengthen the Messenger of Allah sallallahu alayhi wa sallam was fulfilled.
➋. Memorizing the Qur’an, understanding it, and acting upon it to bring about a complete transformation in one’s way of life was only possible in this manner.
➌. It was also intended to provide timely answers to the objections of the disbelievers and to clarify the reality of their demands.
4.
From other narrations, it is known that the beginning of revelation was with: ﴿Iqra’ bismi rabbika allathee khalaq﴾, after which the series of revelation was halted; then, with ﴿Ya ayyuhal muddaththir﴾, the continuous revelation began again.