Surah Ash-Shura (42) — Ayah 13

13. He has ordained for you [14] the same religion which He enjoined upon Noah, and that which We have revealed to you, and that which We enjoined upon Abraham [15], Moses, and Jesus: "Establish the religion and do not be divided [16] therein." What you call the polytheists to is hard [17] for them. Allah chooses for Himself whom He wills, and guides to Himself whoever turns to Him.

[14]
The Difference Between Deen and Shari’ah and Examples of Mutable Rulings:

In this verse, the word "shar‘" appears, and the word "shari‘ah" is derived from it. The other word is "deen." And from ﴿مِنَ الدِّيْنِ﴾, it is understood that shari‘ah is also a part of deen. We present this distinction here with some clarification: The word "deen" has a very broad meaning. Briefly, it is used in four senses:
(1) The complete and perfect political and legal sovereignty of Allah
(2) The complete servitude and worship of man
(3) The law of reward and punishment or national penal code
(4) The power to enforce the law of reward and punishment
Then, sometimes this word is used in one meaning and sometimes in more than one meaning. Now, the requirement of deen is that Allah commands His servants to do certain things, forbids them from certain actions, and whoever acts according to these commands is given a good reward, and whoever disobeys is punished. Thus, such commands that have remained unchanged from our master Adam ؑ to our master Muhammad ﷺ are the real deen, for example: the prohibition of shirk, the Hereafter and its accountability, the command to establish prayer and pay zakat, abstaining from unjust killing, theft, adultery, and indecency, etc. And the literal meaning of shar‘ is to determine a clear path (Mufradat al-Qur’an), and shari‘ah refers to those rulings that change according to the needs of the time and circumstances. For example, in the progeny of our master Adam ؑ, marriage between brother and sister was permissible, and this was a matter of necessity, which was later declared forbidden in subsequent shari‘ahs. Our master Ya‘qub ؑ had two real sisters in his wedlock, which were later forbidden in subsequent shari‘ahs. Similarly, in that era, prostration of respect was permissible, which was later forbidden. In previous shari‘ahs, benefiting from war booty was impermissible, which was made lawful for the Muslim Ummah. In previous shari‘ahs, the number of prayers, their method of performance, the rate of zakat, and the number of fasts were completely different from our present shari‘ah. In short, there are countless such examples. The difference between deen and shari‘ah has been clarified by the Messenger of Allah ﷺ himself in these words: "All the Prophets are paternal brothers. Their mothers (shari‘ahs) are different, but their father (deen) is one." [بخاری۔ کتاب الانبیاء ۔ باب واذکر فی الکتاب مریم]
Thus, the name of the principles and fundamental rulings is deen, and this part of deen is immutable. The second part is that in which changes have occurred in the details of these fundamental rulings. This mutable part is called shari‘ah. Here, it should be kept in mind and well understood that although the shari‘ah of a law-giving Prophet was different, it was still a part of that specific Prophet’s deen. And another noteworthy point is that since you (Muhammad ﷺ) are the last Prophet, the shari‘ah given to you is now also immutable, and the solution to the changing needs of the times will now be sought from the complete Islamic shari‘ah through ijtihad.

[15] In this verse, five Ulul-‘Azm Prophets are mentioned. The first law-giving Prophet was Nuh (Noah) عليه السلام, so he is mentioned first, and the last was Muhammad, the Messenger of Allah ﷺ, then he was mentioned. Then, in the intervening period, three law-giving Prophets—our master Ibrahim, our master Musa, and our master ‘Isa (peace be upon them)—are mentioned. And it is explained that just as We revealed the deen along with the shari‘ah to the previous Prophets with clarity, in the same way, revelation is being sent to you in this manner—that is, both the immutable part of deen and the mutable part, or shari‘ah. Then, sometimes the word deen is applied only to the immutable part of deen, as is clear from the above hadith.

[16] That is, all the Prophets were given deen and shari‘ah with the emphasis that this deen should be upheld. By "upheld" is meant that first, they themselves should implement its rulings, then enforce these rulings among the believers. And in the immutable principles of deen—that is, tawheed and the Hereafter, etc., which have been mentioned above—there should be no disagreement. Although the apparent addressees of this sentence seem to be the Prophets, in reality, the addressees are the followers of those Prophets, and this style is for further emphasis, because the very mission of the Prophets is to end previous disagreements, let alone introduce new ones.

[17] That is, the same tawheed and accountability of the Day of Judgment, which has been the immutable part of the deen of all previous Prophets and in which there could be no room for disagreement—when the polytheists of Makkah are invited to this, it is burdensome for them. That which, from our master Adam ؑ and our master Nuh ؑ until today, was rational and the unanimously agreed teaching of all Prophets, now seems heavy to them. And by differing from this fundamental teaching, they have become its opponents. In other words, their ignorance and wretchedness have reached their limit. And the reality is that only the person who himself seeks guidance and turns to Allah can benefit from this simple and pure teaching. The more a person turns to Allah, the more he will benefit from Allah’s guidance.