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

الترهيب من التهاجر والتشاحن والتدابر

Discouragement of boycotting, mutual-hatred, and turning backs on one another.

Source: al-Targhīb wal-Tarhīb 3/454

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

لَا تَبَاغَضُوا وَلَا تَحَاسَدُوا وَلَا تَدَابَرُوا وَكُونُوا عِبَادَ اللَّهِ إِخْوَانًا وَلَا يَحِلُّ لِمُسْلِمٍ أَنْ يَهْجُرَ أَخَاهُ فَوْقَ ثَلَاثٍ

Do not hate each other, do not envy each other, do not turn away from each other, but rather be servants of Allah as brothers. It is not lawful for a Muslim to boycott his brother for more than three days.

Source: Ṣaḥīḥ al-Bukhārī 5718, Grade: Muttafaqun Alayhi

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

لَا يَحِلُّ لِمُسْلِمٍ أَنْ يَهْجُرَ أَخَاهُ فَوْقَ ثَلَاثِ لَيَالٍ يَلْتَقِيَانِ فَيُعْرِضُ هَذَا وَيُعْرِضُ هَذَا وَخَيْرُهُمَا الَّذِي يَبْدَأُ بِالسَّلَامِ

It is not lawful for a Muslim to boycott his brother for more than three nights, such that they meet each other and turn away. The better of the two is the one who initiates the greeting of peace.

Source: Ṣaḥīḥ al-Bukhārī 5727, Grade: Muttafaqun Alayhi

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

لَا يَحِلُّ لِمُسْلِمٍ أَنْ يَهْجُرَ أَخَاهُ فَوْقَ ثَلَاثٍ فَمَنْ هَجَرَ فَوْقَ ثَلَاثٍ فَمَاتَ دَخَلَ النَّارَ

It is not lawful for a Muslim to boycott his brother for more than three days. Whoever boycotts for more than three days and dies, he will enter Hellfire.

Source: Sunan Abī Dāwūd 4914, Grade: Sahih

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

لَا يَكُونُ لِمُسْلِمٍ أَنْ يَهْجُرَ مُسْلِمًا فَوْقَ ثَلَاثَةٍ فَإِذَا لَقِيَهُ سَلَّمَ عَلَيْهِ ثَلَاثَ مِرَارٍ كُلُّ ذَلِكَ لَا يَرُدُّ عَلَيْهِ فَقَدْ بَاءَ بِإِثْمِهِ

A Muslim may not boycott another Muslim for more than three days. Then, if he meets him, greets him with peace three times, and he receives no response, the sin falls back on the one still boycotting.

Source: Sunan Abī Dāwūd 4913, Grade: Hasan

Hisham ibn ‘Amir reported: The Messenger of Allah, peace and blessings be upon him, said:

لَا يَحِلُّ لِمُسْلِمٍ أَنْ يَهْجُرَ مُسْلِمًا فَوْقَ ثَلَاثِ لَيَالٍ فَإِنَّهُمَا نَاكِبَانِ عَنْ الْحَقِّ مَا دَامَا عَلَى صُرَامِهِمَا وَأَوَّلُهُمَا فَيْئًا يَكُونُ سَبْقُهُ بِالْفَيْءِ كَفَّارَةً لَهُ وَإِنْ سَلَّمَ فَلَمْ يَقْبَلْ وَرَدَّ عَلَيْهِ سَلَامَهُ رَدَّتْ عَلَيْهِ الْمَلَائِكَةُ وَرَدَّ عَلَى الْآخَرِ الشَّيْطَانُ وَإِنْ مَاتَا عَلَى صُرَامِهِمَا لَمْ يَدْخُلَا الْجَنَّةَ جَمِيعًا أَبَدًا

It is not lawful for a Muslim to boycott another Muslim for longer than three nights. Verily, they are both diverting from the truth as long as they are divided. The first of them to return will have his sin expiated by his initiative in returning. If he greets him with peace and he does not accept it, and he rejects his offer of peace, the angels will respond to his greeting of peace and Satan will respond to the other. If they both die while they are divided, they will never enter Paradise together.

Source: Musnad Aḥmad 15824, Grade: Sahih

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

لَا يَحِلُّ الْهَجْرُ فَوْقَ ثَلَاثَةِ أَيَّامٍ فَإِنْ الْتَقَيَا فَسَلَّمَ أَحَدُهُمَا عَلَى الْآخَرِ فَرَدَّ عَلَيْهِ الْآخَرُ السَّلَامَ اشْتَرَكَا فِي الْأَجْرِ وَإِنْ أَبَى الْآخَرُ أَنْ يَرُدَّ السَّلَامَ بَرِئَ هَذَا مِنَ الْإِثْمِ وَبَاءَ بِهِ الْآخَرُ وَقَدْ خَشِيتُ إِنْ مَاتَا وَهُمَا مُتَهَاجِرَانِ أَنْ لَا يَجْتَمِعَا فِي الْجَنَّةِ

It is not lawful to boycott for more than three days. If the two meet and one greets the other with peace and receives a response, they will share the reward. If the other refuses to return his greeting, he is free of sin and it backfires against the one boycotting. I fear that if the two die while boycotting each other, they will not be together in Paradise.

Source: al-Mu’jam al-Awsaṭ 8925, Grade: Sahih li ghayrihi

Fadalah ibn ‘Ubayd reported: The Messenger of Allah, peace and blessings be upon him, said:

مَنْ هَجَرَ أَخَاهُ فَوْقَ ثَلَاثٍ فَهُوَ فِي النَّارِ إِلَّا أَنْ يَتَدَارَكَهُ اللَّهُ بِكَرَمِهِ

Whoever boycotts his brother for more than three days, he is in the Hellfire unless the generosity of Allah reaches him.

Source: al-Mu’jam al-Kabīr 815, Grade: Sahih

Abu Khirash al-Sulami reported: The Prophet, peace and blessings be upon him, said:

مَنْ هَجَرَ أَخَاهُ سَنَةً فَهُوَ كَسَفْكِ دَمِهِ

Whoever boycotts his brother for a year, it is as if he has shed his blood.

Source: Sunan Abī Dāwūd 4915, Grade: Sahih

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

إِنَّ الشَّيْطَانَ قَدْ أَيِسَ أَنْ يَعْبُدَهُ الْمُصَلُّونَ فِي جَزِيرَةِ الْعَرَبِ وَلَكِنْ فِي التَّحْرِيشِ بَيْنَهُمْ

Verily, Satan has lost hope that those who pray on the Arabian Peninsula will ever worship him, so instead he incites discord between them.

Source: Ṣaḥīḥ Muslim 2812, Grade: Sahih

Yazid ibn Wahb reported: Abdullah ibn Mas’ud, may Allah be pleased with him, said:

لَا يَتَهَاجَرْ رَجُلَانِ قَدْ دَخَلَا فِي الْإِسْلَامِ إِلَّا خَرَجَ أَحَدُهُمَا مِنْهُ حَتَّى يَرْجِعَ وَرُجُوعُهُ أَنْ يَأْتِيَهُ فَيُسَلِّمَ عَلَيْهِ

No two men who have entered Islam boycott each other but that one of them has left it until he returns. His return to Islam is going to him and greeting him with peace.

Source: al-Mu’jam al-Kabīr 8904, Grade: Jayyid

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

تُفْتَحُ أَبْوَابُ الْجَنَّةِ يَوْمَ الِاثْنَيْنِ وَيَوْمَ الْخَمِيسِ فَيُغْفَرُ لِكُلِّ عَبْدٍ لَا يُشْرِكُ بِاللَّهِ شَيْئًا إِلَّا رَجُلًا كَانَتْ بَيْنَهُ وَبَيْنَ أَخِيهِ شَحْنَاءُ فَيُقَالُ أَنْظِرُوا هَذَيْنِ حَتَّى يَصْطَلِحَا أَنْظِرُوا هَذَيْنِ حَتَّى يَصْطَلِحَا أَنْظِرُوا هَذَيْنِ حَتَّى يَصْطَلِحَا

The gates of Paradise are opened on Monday and Thursday. Allah forgives every servant who does not associate anything with him, except a man with enmity between himself and his brother. It will be said: Delay these two until they reconcile, delay these two until they reconcile.

Source: Ṣaḥīḥ Muslim 2565, Grade: Sahih

Mu’adh ibn Jabal reported: The Prophet, peace and blessings be upon him, said:

يَطْلُعُ اللَّهُ إِلَى خَلْقِهِ فِي لَيْلَةِ النِّصْفِ مِنْ شَعْبَانَ فَيَغْفِرُ لِجَمِيعِ خَلْقِهِ إِلا لِمُشْرِكٍ أَوْ مُشَاحِنٍ

Allah looks down at his creation on the middle night of Sha’ban and he forgive all of his creatures, except for an idolater or one harboring hatred.

Source: Ṣaḥīḥ Ibn Ḥibbān 5782, Grade: Sahih

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

إِنَّ اللَّهَ لَيَطَّلِعُ فِي لَيْلَةِ النِّصْفِ مِنْ شَعْبَانَ فَيَغْفِرُ لِجَمِيعِ خَلْقِهِ إِلَّا لِمُشْرِكٍ أَوْ مُشَاحِنٍ

Verily, Allah looks down in middle night of Sha’ban and he forgives all of his creatures, except for an idolater or one harboring hatred.

Source: Sunan Ibn Mājah 1390, Grade: Hasan

Abu Tha’labah reported: The Prophet, peace and blessings be upon him, said:

يَطَّلِعُ اللَّهُ عَلَى عِبَادِهِ لَيْلَةَ النِّصْفِ مِنْ شَعْبَانَ فَيَغْفِرُ لِلْمُؤْمِنِينَ وَيُمْهِلُ الْكَافِرِينَ وَيَدَعُ أَهْلَ الْحِقْدِ بِحِقْدِهِمْ حَتَّى يَدَعُوهُ

Allah looks down upon his servants in the middle night of Sha’ban. He forgives the believers, he gives respite to the unbelievers, and he abandons the people of malice to their malice until they leave it.

Source: al-Mu’jam al-Kabīr 590, Grade: Sahih li ghayrihi