Al-Mundhiri recorded the following chapter in his book Al-Targhib wal-Tarhib:

الترهيب من ترك السنة وارتكاب البدع والأهواء

Discouragement of abandoning the Sunnah and committing heretical innovations and indulging in lowly desires.

Source: al-Targhīb wal-Tarhīb 1/83

Aisha reported: The Messenger of Allah, peace and blessings be upon him, said:

مَنْ أَحْدَثَ فِي أَمْرِنَا هَذَا مَا لَيْسَ فِيهِ فَهُوَ رَدٌّ

Whoever innovates into this matter of ours that which does not belong to it, it will be rejected.

Source: Ṣaḥīḥ al-Bukhārī 2550, Grade: Muttafaqun Alayhi

In another narration, the Prophet said:

مَنْ عَمِلَ عَمَلًا لَيْسَ عَلَيْهِ أَمْرُنَا فَهُوَ رَدٌّ

Whoever performs a deed that is not in accordance with our matter will have it rejected.

Source: Ṣaḥīḥ Muslim 1718, Grade: Sahih

Jabir ibn Abdullah reported: The Messenger of Allah, peace and blessings be upon him, said:

مَنْ يَهْدِهِ اللَّهُ فَلَا مُضِلَّ لَهُ وَمَنْ يُضْلِلْهُ فَلَا هَادِيَ لَهُ إِنَّ أَصْدَقَ الْحَدِيثِ كِتَابُ اللَّهِ وَأَحْسَنَ الْهَدْيِ هَدْيُ مُحَمَّدٍ وَشَرُّ الْأُمُورِ مُحْدَثَاتُهَا وَكُلُّ مُحْدَثَةٍ بِدْعَةٌ وَكُلُّ بِدْعَةٍ ضَلَالَةٌ وَكُلُّ ضَلَالَةٍ فِي النَّارِ

Whomever Allah guides, no one can lead him astray. Whomever Allah sends astray, no one can guide him. The truest word is the Book of Allah and the best guidance is the guidance of Muhammad. The most evil matters are those that are newly invented, for every newly invented matter is an innovation. Every innovation is misguidance, and every misguidance is in the Hellfire.

Source: Sunan al-Nasā’ī 1578, Grade: Sahih

Mu’awiyah reported: The Messenger of Allah, peace and blessings be upon him, said, “

أَلَا إِنَّ مَنْ قَبْلَكُمْ مِنْ أَهْلِ الْكِتَابِ افْتَرَقُوا عَلَى ثِنْتَيْنِ وَسَبْعِينَ مِلَّةً وَإِنَّ هَذِهِ الْمِلَّةَ سَتَفْتَرِقُ عَلَى ثَلَاثٍ وَسَبْعِينَ ثِنْتَانِ وَسَبْعُونَ فِي النَّارِ وَوَاحِدَةٌ فِي الْجَنَّةِ وَهِيَ الْجَمَاعَةُ

No doubt, the people of the Book before you split into seventy-two sects and this religion will split into seventy-three sects; seventy-two will be in the Hellfire and one will be in Paradise. It is the united community.

In another narration, the Prophet said:

وَإِنَّهُ سَيَخْرُجُ مِنْ أُمَّتِي أَقْوَامٌ تَجَارَى بِهِمْ تِلْكَ الْأَهْوَاءُ كَمَا يَتَجَارَى الْكَلْبُ لِصَاحِبِهِ

Verily, there will emerge some people in my nation who will be infected by these vain desires, just as rabies infects its patient.

Source: Sunan Abī Dāwūd 4597, Grade: Sahih

Abu Barzah reported: The Prophet, peace and blessings be upon him, said:

إِنَّ مِمَّا أَخْشَى عَلَيْكُمْ شَهَوَاتِ الْغَيِّ فِي بُطُونِكُمْ وَفُرُوجِكُمْ وَمُضِلَّاتِ الْهَوَى

Verily, among what I fear most for you are seductive temptations in your stomachs and passions, and the misguidance of whims.

Source: Musnad Aḥmad 19274, Grade: Sahih

Anas ibn Malik reported: The Prophet, peace and blessings be upon him, said:

ثَلاثٌ مُهْلِكَاتٌ شُحٌّ مُطَاعٌ وَهَوًى مُتَّبَعٌ وَإِعْجَابُ الْمَرْءِ بِنَفْسِهِ مِنَ الْخُيَلاءِ وَثَلاثٌ مُنْجِيَاتٌ الْعَدْلُ فِي الرِّضَا وَالْغَضَبِ وَالْقَصْدُ فِي الْغِنَى وَالْفَاقَةِ وَمَخَافَةُ اللَّهِ فِي السِّرِّ وَالْعَلانِيَةِ

Three are destructive vices: greed that is obeyed, whims that are followed, and a man impressed with himself. Three are salvific virtues: justice in a time of pleasure or anger, moderation in a time of wealth or poverty, and the fear of Allah in public and in private.

Source: al-Mu’jam al-Awsaṭ 5598, Grade: Hasan li ghayrihi

Anas ibn Malik reported: The Messenger of Allah, peace and blessings be upon him, said:

إِنَّ اللَّهَ حَجَبَ التَّوْبَةَ عَنْ صَاحِبِ كُلِّ بِدْعَةٍ

Verily, Allah blocks the repentance of all who commit heretical innovations.

Source: al-Mu’jam al-Awsaṭ 4204, Grade: Sahih

In another narration, the Prophet said:

حَتَّى يَدَعَ بِدْعَتَهُ

Until he abandons his innovation.

Source: Sunan Ibn Mājah 50

Al-‘Irbad ibn Sariyah reported: The Messenger of Allah, peace and blessings be upon him, said:

وَإِيَّاكُمْ وَمُحْدَثَاتِ الْأُمُورِ فَإِنَّهَا ضَلَالَةٌ فَمَنْ أَدْرَكَ ذَلِكَ مِنْكُمْ فَعَلَيْهِ بِسُنَّتِي وَسُنَّةِ الْخُلَفَاءِ الرَّاشِدِينَ الْمَهْدِيِّينَ عَضُّوا عَلَيْهَا بِالنَّوَاجِذِ

Beware of newly invented matters, for they are misguidance. Whoever sees them must adhere to my Sunnah and the Sunnah of the upright, guided Caliphs. Bite onto it with your back teeth.

Source: Sunan al-Tirmidhī 2676, Grade: Sahih

Abdullah ibn Amr reported: The Prophet, peace and blessings be upon him, said:

إِنَّ لِكُلِّ عَمَلٍ شِرَّةً وَلِكُلِّ شِرَّةٍ فَتْرَةٌ فَمَنْ كَانَتْ شِرَّتُهُ إِلَى سُنَّتِي فَقَدْ أَفْلَحَ وَمَنْ كَانَتْ فَتْرَتُهُ إِلَى غَيْرِ ذَلِكَ فَقَدْ هَلَكَ

Verily, every deed has an enthusiasm and every enthusiasm has a limit. Whoever is enthusiastic for my Sunnah will have succeeded, but whoever is enthusiastic for something else has been ruined.

Source: Musnad Aḥmad 6725, Grade: Sahih

Abu Huraira reported: The Prophet, peace and blessings be upon him, said:

إِنَّ لِكُلِّ شَيْءٍ شِرَّةً وَلِكُلِّ شِرَّةٍ فَتْرَةً فَإِنْ كَانَ صَاحِبُهَا سَدَّدَ وَقَارَبَ فَارْجُوهُ وَإِنْ أُشِيرَ إِلَيْهِ بِالْأَصَابِعِ فَلَا تَعُدُّوهُ

Verily, everything has a zeal and every zeal has a limit. Whoever does so properly and moderately, he will have hope for success. Whoever earns fingers of accusation, he will not be deemed worthy.

Source: Sunan al-Tirmidhī 2453, Grade: Sahih

Anas ibn Malik reported: The Prophet, peace and blessings be upon him, said:

مَنْ رَغِبَ عَنْ سُنَّتِي فَلَيْسَ مِنِّي

Whoever does not desire my Sunnah is not part of me.

Source: Ṣaḥīḥ Muslim 1401, Grade: Sahih

Al-‘Irbad ibn Sariyah reported: The Prophet, peace and blessings be upon him, said:

قَدْ تَرَكْتُكُمْ عَلَى الْبَيْضَاءِ لَيْلُهَا كَنَهَارِهَا لاَ يَزِيغُ عَنْهَا بَعْدِي إِلاَّ هَالِكٌ

I have left you upon a clear path, its clarity is the same by night or day. No one deviates from it after me but the he will be ruined.

Source: Sunan Ibn Mājah 44, Grade: Sahih