Judge people of book by their shariah

And We have sent down to you (O Muhammad SAW) the Book (this Qur'ân) in truth, confirming the Scripture that came before it and Muhaymin (trustworthy in highness and a witness) over it (old Scriptures)[]. So judge among them by what Allâh has revealed, and follow not their vain desires, diverging away from the truth that has come to you. To each among you, We have prescribed a law and a clear way. If Allâh had willed, He would have made you one nation, but that (He) may test you in what He has given you; so compete in good deeds. The return of you (all) is to Allâh; then He will inform you about that in which you used to differ


And so judge (you O Muhammad SAW) among them by what Allâh has revealed and follow not their vain desires, but beware of them lest they turn you (O Muhammad SAW) far away from some of that which Allâh has sent down to you. And if they turn away, then know that Allâh's Will is to punish them for some sins of theirs. And truly, most of men are Fâsiqûn (rebellious and disobedient to Allâh).

Do they then seek the judgement of (the days of) Ignorance?[i.e judgement from other than the word of Allah] And who is better in judgement than Allâh for a people who have firm Faith.

Al maeda 48-50