Al-Jawāb as-Sahīh li-man baddala dīn al-Masīh - Ibn Taimiya - (2/240)

And the Exalted also says:

“The Messenger has believed in what has been sent down to him from his Lord, and so have the believers. Each of them believes in Allah, His angels, His books, and His messengers; ‘We make no distinction between any of His messengers.’” ⦗2:285⦘

In another canonical reading the phrase appears as “His book and His messengers,” and the two readings agree in meaning.

He, exalted is He, likewise says:

“Mankind was once a single community,” ⦗2:213⦘

meaning that they later fell into disagreement, as He states in another surah: “Mankind were but one community, then they differed.” So when the children of Adam differed, Allah sent the prophets as bearers of glad tidings and as warners, and He sent down with them the Book.

This applies to every scripture that Allah has revealed, so that Allah—and His Book—may judge between people in truth. The true Judge among humankind is Allah, and His judgment is found in His revealed books. For this reason Allah commanded the believers that if they dispute about anything, they should refer it back to Allah and the Messenger.

Referring it back to Allah means referring it back to His Book; thus He ordered them to return to His Book and to His Messenger. The Exalted has condemned those who do not seek judgment from His Book and His Messenger, saying:

وَقَالَ - تَعَالَى -: {آمَنَ الرَّسُولُ بِمَا أُنْزِلَ إِلَيْهِ مِنْ رَبِّهِ وَالْمُؤْمِنُونَ كُلٌّ آمَنَ بِاللَّهِ وَمَلَائِكَتِهِ وَكُتُبِهِ وَرُسُلِهِ لَا نُفَرِّقُ بَيْنَ أَحَدٍ مِنْ رُسُلِهِ} [البقرة: ٢٨٥] وَفِي الْقِرَاءَةِ الْأُخْرَى وَكِتَابِهِ وَرُسُلِهِ وَكِلَا الْقِرَاءَتَيْنِ مُوَافِقَةٌ لِلْأُخْرَى وَقَوْلُهُ - تَعَالَى -: {كَانَ النَّاسُ أُمَّةً وَاحِدَةً} [البقرة: ٢١٣] أَيْ فَاخْتَلَفُوا بَعْدَ ذَلِكَ ; كَمَا قَالَ: فِي السُّورَةِ الْأُخْرَى وَمَا كَانَ النَّاسُ إِلَّا أُمَّةً وَاحِدَةً فَاخْتَلَفُوا فَلَمَّا اخْتَلَفَ بَنُو آدَمَ بَعَثَ النَّبِيِّينَ مُبَشِّرِينَ وَمُنْذِرِينَ وَأَنْزَلَ مَعَهُمُ الْكِتَابَ. وَذَلِكَ يَتَنَاوَلُ كُلَّ كِتَابٍ أَنْزَلَهُ اللَّهُ لِيَحْكُمَ اللَّهُ وَيَحْكُمَ كِتَابُهُ بَيْنَ النَّاسِ بِالْحَقِّ فَالْحَاكِمُ بَيْنَ النَّاسِ هُوَ اللَّهُ تَعَالَى وَحُكْمُهُ فِي كُتُبِهِ الْمُنَزَّلَةِ فَلِهَذَا أَمَرَ اللَّهُ الْمُؤْمِنِينَ إِذَا تَنَازَعُوا فِي شَيْءٍ أَنْ يَرُدُّوهُ إِلَى اللَّهِ وَالرَّسُولِ. وَالرَّدُّ إِلَى اللَّهِ هُوَ الرَّدُّ إِلَى كِتَابِهِ فَأَمَرَهُمْ بِالرَّدِّ إِلَى كِتَابِهِ وَرَسُولِهِ وَقَدْ ذَمَّ تَعَالَى مَنْ لَمْ يَتَحَاكَمْ إِلَى كِتَابِهِ وَرَسُولِهِ فَقَالَ تَعَالَى: