Al-Jawāb as-Sahīh li-man baddala dīn al-Masīh - Ibn Taimiya - (2/438)

He therefore commanded His Prophet Muhammad—may Allah bless him and grant him peace—to judge according to what Allah had revealed to him, warned him against following their whims, and declared that any judgment contrary to His is the judgment of the Age of Ignorance. Allah, Exalted is He, says: “Is it the judgment of the Age of Ignorance that they seek? Who is better than Allah in judgment for a people who are certain?” ⦗al-Māʾidah 50⦘.

Allah also informed him that He has assigned to the followers of the Torah, the Gospel, and the Quran alike a law and a method. Hence His command to rule by what Allah has revealed is universal for the people of the Torah, the Gospel, and the Quran; at no time may anyone judge by anything other than what Allah has sent down. What Allah has revealed is one religion on which all the Scriptures and the messengers agree. They are united in the essentials of faith and the foundations of the Law, even though their particular rulings and paths vary—between what abrogates and what is abrogated—much like the variety that occurs within a single book.

For example, the Muslims were first commanded to face Bayt al-Maqdis (Jerusalem) in prayer, and later they were ordered to face al-Masjid al-Ḥarām (the Sacred Mosque). In both cases they were simply following what Allah—majestic and exalted is He—had revealed.

فَقَدَ أَمَرَ نَبِيَّهُ مُحَمَّدًا - صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ - أَنْ يَحْكُمَ بِمَا أَنْزَلَ اللَّهُ إِلَيْهِ وَحَذَّرَهُ اتِّبَاعَ أَهْوَائِهِمْ وَبَيَّنَ أَنَّ الْمُخَالِفَ لِحُكْمِهِ هُوَ حُكْمُ الْجَاهِلِيَّةِ حَيْثُ قَالَ - تَعَالَى -: {أَفَحُكْمَ الْجَاهِلِيَّةِ يَبْغُونَ وَمَنْ أَحْسَنُ مِنَ اللَّهِ حُكْمًا لِقَوْمٍ يُوقِنُونَ} [المائدة: ٥٠] وَأَخْبَرَهُ تَعَالَى أَنَّهُ جَعَلَ لِكُلٍّ مِنْ أَهْلِ التَّوْرَاةِ وَالْإِنْجِيلِ وَالْقُرْآنِ شِرْعَةً وَمِنْهَاجًا، وَأَمْرُهُ تَعَالَى بِالْحُكْمِ بِمَا أَنْزَلَ اللَّهُ أَمْرٌ عَامٌّ لِأَهْلِ التَّوْرَاةِ وَالْإِنْجِيلِ وَالْقُرْآنِ لَيْسَ لِأَحَدٍ فِي وَقْتٍ مِنَ الْأَوْقَاتِ أَنْ يَحْكُمَ بِغَيْرِ مَا أَنْزَلَ اللَّهُ وَالَّذِي أَنْزَلَهُ اللَّهُ هُوَ دِينٌ وَاحِدٌ اتَّفَقَتْ عَلَيْهِ الْكُتُبُ وَالرُّسُلُ وَهُمْ مُتَّفِقُونَ فِي أُصُولِ الدِّينِ وَقَوَاعِدِ الشَّرِيعَةِ وَإِنْ تَنَوَّعُوا فِي الشِّرْعَةِ وَالْمِنْهَاجِ بَيْنَ نَاسِخٍ وَمَنْسُوخٍ فَهُوَ شَبِيهٌ بِتَنَوُّعِ حَالِ الْكِتَابِ الْوَاحِدِ، فَإِنَّ الْمُسْلِمِينَ كَانُوا أَوَّلًا مَأْمُورِينَ بِالصَّلَاةِ لِبَيْتِ الْمَقْدِسِ، ثُمَّ أُمِرُوا أَنْ يُصَلُّوا إِلَى الْمَسْجِدِ الْحَرَامِ وَفِي كِلَا الْأَمْرَيْنِ إِنَّمَا اتَّبَعُوا مَا أَنْزَلَ اللَّهُ - عَزَّ وَجَلَّ -.