Completeness of the Qur'an

أَفَغَيْرَ ٱللَّهِ أَبْتَغِى حَكَمًا وَهُوَ ٱلَّذِىٓ أَنزَلَ إِلَيْكُمُ ٱلْكِتَـٰبَ مُفَصَّلًا ۚ وَٱلَّذِينَ ءَاتَيْنَـٰهُمُ ٱلْكِتَـٰبَ يَعْلَمُونَ أَنَّهُۥ مُنَزَّلٌ مِّن رَّبِّكَ بِٱلْحَقِّ ۖ فَلَا تَكُونَنَّ مِنَ ٱلْمُمْتَرِينَ

[Say], "Then is it other than Allāh I should seek as judge while it is He who has revealed to you the Book [i.e., the Qur’ān] explained in detail?" And those to whom We [previously] gave the Scripture know that it is sent down from your Lord in truth, so never be among the doubters.

وَيَوْمَ نَبْعَثُ فِى كُلِّ أُمَّةٍ شَهِيدًا عَلَيْهِم مِّنْ أَنفُسِهِمْ ۖ وَجِئْنَا بِكَ شَهِيدًا عَلَىٰ هَـٰٓؤُلَآءِ ۚ وَنَزَّلْنَا عَلَيْكَ ٱلْكِتَـٰبَ تِبْيَـٰنًا لِّكُلِّ شَىْءٍ وَهُدًى وَرَحْمَةً وَبُشْرَىٰ لِلْمُسْلِمِينَ

And [mention] the Day when We will resurrect among every nation a witness over them from themselves [i.e., their prophet]. And We will bring you, [O Muḥammad], as a witness over these [i.e., your nation]. And We have sent down to you the Book as clarification for all things and as guidance and mercy and good tidings for the Muslims.