Praise be to Allah.
The division of the Qur’an into ajzaa’ (sing. juz’), ahzaab (sing. hizb) and arbaa‘ (sing. rub‘) [these are names of portions into which the Qur’an is divided] is something that was developed and agreed upon later on by scholars, and is based on their own ijtihaad. Hence scholars may differ in how they divide it, each according to what suited him and what he preferred, and according to what he thought most beneficial and easier for people. But the well-known division [of the Qur’an] that was narrated from the Sahaabah (may Allah be pleased with them) is that which was narrated by Aws ibn Hudhayfah, who said:
I asked the Companions of the Messenger of Allah (blessings and peace of Allah be upon him) how they divided the Qur’an [into portions]. They said: Three, five, seven, nine, eleven, thirteen, and hizb al-mufassal on its own. Narrated by Abu Dawood (1393).
What this means is:
Three soorahs after al-Faatihah, namely: al-Baqarah, Aal ‘Imraan and an-Nisaa’.
Then five soorahs, namely: al-Maa’idah, al-An‘aam, al-A‘raaf, al-Anfaal, and at-Tawbah.
Then seven soorahs, namely: Yoonus, Hood, Yoosuf, ar-Ra‘d, Ibraaheem, al-Hijr, and an-Nahl.
Then nine soorahs, namely: Soorat al-Isra’, al-Kahf, Maryam, Taa-Haa, al-Anbiya’, al-Hajj, al-Mu’minoon, an-Noor and al-Furqaan.
Then eleven soorahs, namely ash-Shu‘ara’, an-Naml, al-Qasas, al-‘Ankaboot, ar-Room, Luqmaan, as-Sajdah, al-Ahzaab, Saba’, Faatir and Yaa-Seen.
Then thirteen soorahs, namely as-Saafaat, Saad, az-Zumar, the seven soorahs beginning with Haa-Meem, Muhammad, al-Fath, and al-Hujuraat.
Then the rest, from Soorat Qaaf to an-Naas.
Az-Zarqaani said in Manaahil al-‘Irfaan fi ‘Uloom al-Qur’an (1/238), under the heading Division of the Qur’an into portions:
The Uthmaani mus-hafs were not divided into portions as we are discussing here, and they had no dots or vowel marks. With the passage of time, people began to come up with various ways of writing the Mus-haf and dividing it into portions, and they came up with a number of systems. Some of them divided the Qur’an into thirty sections, each of which they called a juz’ (pl. ajzaa’), so that when this word was used without qualification and someone said, I read a juz’ of the Qur’an, nothing would spring to mind except the idea that he had read one of the thirty parts into which they divided the Mus-haf.
Some people divided each juz’ into two parts, called hizb (pl. ahzaab), and some divided each hizb into four parts called rub‘ (pl. arbaa‘) [which literally means “quarter”].
Some people put the word khams (five) after every five verses of a soorah, and the word ‘ashr (ten) after every ten verses. After the next five verses they repeated the word khams, and after ten they repeated the word ‘ashr, and so on until the end of the soorah.
Instead of writing the word khams, some of them wrote the Arabic letter kha’, and instead of writing the word ‘ashr, they wrote the Arabic letter ‘ayn.
Some people wrote the number of the verse at the beginning of each verse, and some wrote a symbol without a number.
Some of them put a heading at the beginning of each soorah, showing the name of the soorah, the number of its verses and whether they were Makki or Madani, and so on.
The scholars have spoken at length about that and whether it is permissible but makrooh, or permissible but not makrooh. However there may be some leniency concerning this matter, so long as the aim is to make things easier for people, and so long as it is far removed from causing confusion, going to extremes or introducing any element that is alien to and inappropriate for the Qur’an. And we ask Allah for guidance. End quote.
With regard to the division into portions that is found nowadays in the Mus-hafs, there is no certainty as to who was the first one to introduce it. But what was narrated by some of the scholars is that the first one to do that was al-Hajjaaj ibn Yoosuf ath-Thaqafi (d. 110 AH), and that the basis for this division was the number of letters.
Shaykh al-Islam Ibn Taymiyah said in Majmoo‘ al-Fataawa (13/409):
It is known that initially the Qur’an was divided on the basis of counting the number of letters into twenty-eight parts, and thirty parts and sixty parts. That was done with a mark to indicate the beginning of a juz’ or hizb in the soorah, or within a narrative, and the like. That was at the time of al-Hajjaaj and afterwards. It was narrated that al-Hajjaaj issued orders that that be done, and from Iraq this practice spread everywhere, but the people of Madinah did not know about that. Even though division on the basis of the number of letters was something introduced during the era of al-Hajjaaj in Iraq, it is well-known that before that, the Sahaabah at the time of the Prophet (blessings and peace of Allah be upon him) and after that had a different way of dividing the Qur’an. They used to divide it sometimes on the basis of the number of verses, so they would say: fifty verses, or sixty verses; and sometimes it would be based on the soorahs, but the idea that they divided it into seven parts on the basis of the number of verses was not narrated or mentioned by anyone, so they must have divided it on the basis of the soorahs, not the verses. End quote.
Ibn Taymiyah (may Allah have mercy on him) said in Majmoo‘ al-Fataawa (13/410-416):
What the Sahaabah did is best, for a number of reasons:
1. This newly-introduced way of dividing the Qur’an always leads to pausing at some phrase that is connected to what comes after it, which may even lead to an interruption in mid-phrase. Thus the reader, on the next day, starts partway through a sentence, as in the verses “And [also prohibited to you are all] married women except those your right hands possess” [an-Nisa’ 4:24], “And whoever of you devoutly obeys Allah and His Messenger” [al-Ahzaab 33:31], and so on.
2. The Prophet (blessings and peace of Allah be upon him) and his companions usually recited an entire soorah such as Qaaf and the like in the prayer. As reciting from the end or middle of a soorah, that was not a common practice among them, hence it is something to be avoided, as it is makrooh. Concerning that there is a well-known difference of opinion in the madhhab of Ahmad and among other scholars. One of the most appropriate views is the view of those who say that it is makrooh to do that regularly, but it is not makrooh if it is done occasionally, so as to avoid going against the Sunnah and the practice of the early generations, namely the Sahaabah and Taabi‘een.
Having said that, we may note that this way of dividing the Qur’an is more contrary to the Sunnah than starting the recitation in prayer from the end or middle of a soorah.
Whatever the case, undoubtedly dividing the Qur’an into portions that is in accordance with the practice of the Prophet (blessings and peace of Allah be upon him) and the Sahaabah in recitation is more appropriate.
The point is that dividing the Qur’an on the basis of complete soorahs is more appropriate then dividing it in such a way that there is an interruption in the middle of a soorah.
3. With regard to the newly-introduced way of dividing the Qur’an, in which there is no way to make the number of letters in each portion equal, that is because the letters as pronounced may differ from the letters that are written, hence dividing it on the basis of letters is approximate and is not precise. That is akin to dividing it on the basis of soorahs, which is also approximate. When dividing it into groups of seven soorahs, some soorahs may be longer than others in terms of letters, and in that there is a great interest to be served by continuing to read until the meaning is complete, and to begin reading a soorah from the beginning, as Allah revealed it, and to end it as Allah ended it, and continuing to read in order to understand the meaning conveyed in each soorah. This is something that you do not find in other ways of dividing the Qur’an. End quote.
The scholars of the Permanent Committee for Ifta’ were asked:
Is it permissible to divide the Qur’an – when reciting it – because that would lead to distorting the intended meaning, and because of it there may be some addition or omission? This is what we see in some regions of North Africa. Is that permissible?
We do not know of any evidence for dividing the Qur’an into portions as shown in the margins of the Mus-hafs that are in circulation among people today. What was narrated from the Sahaabah (may Allah be pleased with them) concerning that is the report narrated by Aws ibn Hudhayfah, who said: I asked the companions of the Messenger of Allah (blessings and peace of Allah be upon him) how they used to divide the Qur’an. They said: Three, five, seven, nine, eleven, thirteen, and hizb al-mufassal on its own. End quote.
Fataawa al-Lajnah ad-Daa’imah (4/30).
Conclusion: The division of the Qur’an that is shown today is based on the number of letters, and it is different from the best way of dividing it, which was the approach of the Sahaabah (may Allah be pleased with them), who did it on the basis of the soorahs. Nevertheless, the matter is broad in scope.
And Allah knows best.