Allah ﷻ said: "What is there after the truth except falsehood?" [Yunus: 32].
And He ﷻ said: "We have neglected nothing in the Book" [Anam: 38].
And He ﷻ said: "If you disagree about anything, refer it to God and the Messenger" [Nisa: 59], meaning the Book and the Sunnah.
And He ﷻ said: "And verily, this is My straight path, so follow it, and do not follow other ways, for they will lead you away from His path" [Anam: 153].
And He ﷻ said: "Say: If you love Allah, follow me, and Allah will love you and forgive your sins" [Al Imran 3:31].
There are many known verses in this context. As for the hadiths, there are very many, and they are well-known, so we shall limit ourselves to mentioning a portion of them.
قَالَ الله تَعَالَى: ﴿فَمَاذَا بَعْدَ الْحَقِّ إِلاَّ الضَّلال﴾ [يونس: ٣٢]،
وَقالَ تَعَالَى: ﴿مَا فَرَّطْنَا فِي الْكِتَابِ مِنْ شَيْء﴾ [الأنعام: ٣٨]،
وَقالَ تَعَالَى: ﴿فَإِنْ تَنَازَعْتُمْ فِي شَيْءٍ فَرُدُّوهُ إِلَى اللهِ وَالرَّسُولِ﴾ [النساء: ٥٩] أيِ الكِتَابِ وَالسُّنَّةِ.
وَقالَ تَعَالَى: ﴿وَأَنَّ هَذَا صِرَاطِي مُسْتَقِيمًا فَاتَّبِعُوهُ وَلا تَتَّبِعُوا السُّبُلَ فَتَفَرَّقَ بِكُمْ عَنْ سَبِيلِهِ﴾ [الأنعام: ١٥٣]،
وَقالَ تَعَالَى: ﴿قُلْ إِنْ كُنْتُمْ تُحِبُّونَ اللهَ فَاتَّبِعُونِي يُحْبِبْكُمُ اللهُ وَيَغْفِرْ لَكُمْ ذُنُوبَكُمْ﴾ [آل عمران:٣١]
وَالآياتُ في البَابِ كَثيرةٌ مَعلُومَةٌ. وَأَمَّا اَلأحادِيثُ فَكَثيرَةٌ جدًا، وَهيَ مَشْهُورَةٌ فَنَقْتَصِرُ عَلَى طَرَفٍ مِنْهَا:
the Messenger of Allah ﷺ said, "Whoever innovates something in this affair of ours that is not from it, then it is rejected."
قَالَ رَسُولُ اللَّهِ ﷺ: «مَنْ أَحْدَثَ فِي أَمْرِنَا هَذَا مَا لَيْسَ فِيهِ فَهُوَ رَدٌّ».
I asked al-Qasim b. Muhammad about a man who has three dwellings and bequeathed one third of each dwelling. He said: All of that is combined into a single dwelling. Then he said: Aishah told me that the Messenger of Allah ﷺ said: “Whoever does a deed that is not in accordance with our command, it is rejected.”
سَأَلْتُ الْقَاسِمَ بْنَ مُحَمَّدٍ عَنْ رَجُلٍ لَهُ ثَلاَثَةُ مَسَاكِنَ فَأَوْصَى بِثُلُثِ كُلِّ مَسْكَنٍ مِنْهَا قَالَ: يُجْمَعُ ذَلِكَ كُلُّهُ فِي مَسْكَنٍ وَاحِدٍ. ثُمَّ قَالَ: أَخْبَرَتْنِي عَائِشَةُ أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ: «مَنْ عَمِلَ عَمَلاً لَيْسَ عَلَيْهِ أَمْرُنَا فَهُوَ رَدٌّ».
When the Messenger of Allah ﷺ delivered a sermon, his eyes would become red, his voice would rise, and his anger would intensify, until it was as though he were warning an army, saying: “An enemy has come upon you in the morning and in the evening.” And he would say: “I have been sent, and the Hour, like these two,” and he would join his index finger and middle finger.
And he would say: “To proceed: indeed, the best speech is the Book of Allah, the best guidance is the guidance of Muhammad, and the worst of matters are newly invented ones; and every innovation is misguidance.” Then he would say: “I am (i.e. following me) is a priority to every believer than his own self. Whoever leaves behind wealth, it is for his family; and whoever leaves behind a debt or dependents in need, then it is ˹a responsibility˺ to me and upon me.”
كَانَ رَسُولُ اللَّهِ ﷺ إِذَا خَطَبَ احْمَرَّتْ عَيْنَاهُ وَعَلاَ صَوْتُهُ وَاشْتَدَّ غَضَبُهُ، حَتَّى كَأَنَّهُ مُنْذِرُ جَيْشٍ يَقُولُ: «صَبَّحَكُمْ وَمَسَّاكُمْ»، وَيَقُولُ: «بُعِثْتُ أَنَا وَالسَّاعَةَ كَهَاتَيْنِ»، وَيَقْرُنُ بَيْنَ إِصْبَعَيْهِ السَّبَّابَةِ وَالْوُسْطَى،
وَيَقُولُ: «أَمَّا بَعْدُ، فَإِنَّ خَيْرَ الْحَدِيثِ كِتَابُ اللَّهِ، وَخَيْرُ الْهُدَى هُدَى مُحَمَّدٍ، وَشَرُّ الأُمُورِ مُحْدَثَاتُهَا، وَكُلُّ بِدْعَةٍ ضَلاَلَةٌ»، ثُمَّ يَقُولُ: «أَنَا أَوْلَى بِكُلِّ مُؤْمِنٍ مِنْ نَفْسِهِ مَنْ تَرَكَ مَالاً فَلأَهْلِهِ، وَمَنْ تَرَكَ دَيْنًا أَوْ ضَيَاعًا فَإِلَىَّ وَعَلَىَّ».
We came to al-Irbad b. Sariyah – one of those concerning whom the verse was revealed: “Nor ˹is there blame˺ upon those who, when they came to you for you to mount them, you said, 'I can find nothing to carry you upon.'” – We greeted ˹him˺ and said, “We have come to you as visitors, to inquire after you, and to seek knowledge.”
al-Irbad said: The Messenger of Allah ﷺ led us in prayer one day, then turned to us and gave us an eloquent admonition that caused the eyes to shed tears and the hearts to tremble. Someone said, “O Messenger of Allah, it is as though this is the admonition of one bidding farewell; so what do you enjoin upon us?”
He said: “I enjoin you to fear Allah, and to listen and obey, even if ˹you are led by˺ an Abyssinian slave. For whoever among you lives after me will see much disagreement. So hold fast to my Sunnah and the Sunnah of the rightly guided and directed caliphs. Hold on to it, and bite onto it with your molar teeth. And beware of newly invented matters, for every newly invented matter is an innovation, and every innovation is misguidance.”
أَتَيْنَا الْعِرْبَاضَ بْنَ سَارِيَةَ وَهُوَ مِمَّنْ نَزَلَ فِيهِ { وَلاَ عَلَى الَّذِينَ إِذَا مَا أَتَوْكَ لِتَحْمِلَهُمْ قُلْتَ لاَ أَجِدُ مَا أَحْمِلُكُمْ عَلَيْهِ } فَسَلَّمْنَا، وَقُلْنَا أَتَيْنَاكَ زَائِرِينَ وَعَائِدِينَ وَمُقْتَبِسِينَ،
فَقَالَ الْعِرْبَاضُ: صَلَّى بِنَا رَسُولُ اللَّهِ ﷺ ذَاتَ يَوْمٍ ثُمَّ أَقْبَلَ عَلَيْنَا، فَوَعَظَنَا مَوْعِظَةً بَلِيغَةً ذَرَفَتْ مِنْهَا الْعُيُونُ وَوَجِلَتْ مِنْهَا الْقُلُوبُ، فَقَالَ قَائِلٌ: يَا رَسُولَ اللَّهِ كَأَنَّ هَذِهِ مَوْعِظَةُ مُوَدِّعٍ فَمَاذَا تَعْهَدُ إِلَيْنَا؟
فَقَالَ: «أُوصِيكُمْ بِتَقْوَى اللَّهِ وَالسَّمْعِ وَالطَّاعَةِ وَإِنْ عَبْدًا حَبَشِيًّا، فَإِنَّهُ مَنْ يَعِشْ مِنْكُمْ بَعْدِي فَسَيَرَى اخْتِلاَفًا كَثِيرًا، فَعَلَيْكُمْ بِسُنَّتِي وَسُنَّةِ الْخُلَفَاءِ الْمَهْدِيِّينَ الرَّاشِدِينَ، تَمَسَّكُوا بِهَا، وَعَضُّوا عَلَيْهَا بِالنَّوَاجِذِ، وَإِيَّاكُمْ وَمُحْدَثَاتِ الأُمُورِ، فَإِنَّ كُلَّ مُحْدَثَةٍ بِدْعَةٌ وَكُلَّ بِدْعَةٍ ضَلاَلَةٌ».