Hadith on Division: They will never enter Paradise together if they remain divided

Hisham ibn Amr reported: The Messenger of Allah, peace and blessings be upon him, said, “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 due to his initiative in returning. If he greets him with peace and he does not accept it, and he rejects his offer of peace, then 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 (authentic) according to Al-Haythami

عَنْ هِشَامِ بْنِ عَامِرٍ قَالَ قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ 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

15824 مسند أحمد أول مسند المدنيين رضي الله عنهم أجمعين

8/69 المحدث الهيثمي خلاصة حكم المحدث رجال أحمد رجال الصحيح في مجمع الزوائد