Thus Allāh and His Messenger (ﷺ) ordered that the rights of the believers be fulfilled by each other, and that those matters which will bring about harmony, love and togetherness be carried out.

Allāh – the One free from all imperfections – said:

فَاتَّقُوا اللَّهَ وَأَصْلِحُوا ذَاتَ بَيْنِكُمْ ۖ ‎﴿١﴾‏

“So have taqwá (fear and obedience) of Allāh and reconcile the differences between yourselves.”
[Al-Anfāl, 8:1]

إِنَّمَا الْمُؤْمِنُونَ إِخْوَةٌ فَأَصْلِحُوا بَيْنَ أَخَوَيْكُمْ ۚ وَاتَّقُوا اللَّهَ لَعَلَّكُمْ تُرْحَمُونَ ‎﴿١٠﴾‏

“Indeed the Believers are but brothers.  Therefore reconcile the differences between your brothers, and fear Allāh so that you may receive mercy. ”
[Al-Ḥujurāt, 49:10]

Imām ʿAbd al-Raḥmān Ibn Nālir as-Saʿdī (d.1376H) – raḥimahullāh – said:

“So this is a knot which Allāh has bound the Believers together with, such that whenever a person is found possessing īmān (faith) in Allāh, His Angels, His Books, His Messengers and the last Day – whether in the eastern or western part of the world – then such a person becomes the brother of the Believers. This brotherhood obligates that the Believers should love for that person that which they love for themselves, and hate for that person that which they hate for themselves. Therefore, the Prophet (ﷺ) said – whilst ordering the brotherhood of īmān (faith): “Do not envy one another. Do not inflate prices upon one another. Do not hate one another. Do not forsake one another. Do not under-cut one another. But be worshippers of Allāh and brothers. The Muslim is the brother of another Muslim; he neither oppresses him, nor humiliates him, nor lies to him, nor holds him in contempt. And piety is right here – and he pointed to his chest three times. It is enough evil for a person to hold his brother Muslim in contempt. The whole of a Muslim for another Muslim is sacred; his blood, his property, and his honour.”¹ And he (ﷺ) said: “The Believer to the Believer is like a solid structure, one part supporting the other.” And he interlaced his fingers to demonstrate this.²

Thus, Allāh and His Messenger (ﷺ) ordered that the rights of the Believers be fulfilled by each other, and that those matters which will bring about harmony, love and togetherness be carried out. All of this is to be done in order to further the rights that they have over one another. So from such rights is that when fighting occurs between them – thereby causing their hearts to separate and to have hatred and to cut-off from each other – then the Believers should bring about reconciliation between their brothers and do that which will remove the enmity. Then Allāh ordered taqwá in general and made the bestowal of His Mercy the consequence of their having taqwá and their fulfilling the rights of the Believers. So He said: “And have taqwá of Allāh in order that you may receive mercy.” Thus, if Allāh’s Mercy is attained, then the good of this world and the Hereafter will also be attained.”³

’Aa‘ishah (raḍī Allāhu ’anhaa) used to say: that when people abandoned acting upon this āyah (verse):

وَإِن طَائِفَتَانِ مِنَ الْمُؤْمِنِينَ اقْتَتَلُوا فَأَصْلِحُوا بَيْنَهُمَا ۖ ﴿٩﴾‏

“When two parties of the Believers fight each other, then make reconciliation between them.”
[Al-Ḥujurāt 49:9]

So when the Muslims began fighting each other, it was obligatory to reconcile them, as Allāh – the Most High – ordered. However, when they did not do this, then fitnah (trials and tribulations) spread, as did ignorance, and this is what caused the differences to continue.⁴

Allāh’s Messenger (ﷺ) said: “Shall I not inform you of something that is greater in degree than (optional) fasting, charity and Prayer?” They said: Indeed inform us. So he said: “It is reconciling the people. For indeed causing corruption between them is the shaver!”⁵

And he (ﷺ) explained this shaving in another saying: “The disease of the people before you has overcome you: namely envy and hatred, and it is the shaver. I do not say that it shaves off the hair. Rather, it shaves off the Religion.”⁶

Endnotes:

1. Related by Muslim (no.2564), from Abū Hurayrah (raḍī Allāhu ʿanhu).
2. Related by al-Bukhārī (no. 481) and Muslim (no. 2585), from Abū Hurayrah (raḍī Allāhu ʿanhu).
3. Taysīr al-Karīm al-Raḥmān (7/133-134) of Imām as-Saʿdī.
4. Related by Ibn Abī al-ʿIzz in Sharḥ al-ʿAqīdah al-Ṭaḥāwiyyah (2/777).  Imām al-Bayhaqī related something similar to this in his Sunan al-Kubrā (8/172).
5. Ṣaḥīḥ: Related by al-Tirmidhī (no. 2640) and Abū Dāwūd (no. 4919), from Abū al-Dardāʾ (raḍī Allāhu ʿanhu). It was authenticated by al-Albānī in Ghāyah al-Marām (no. 414).
6. Ḥasan: Related by al-Tirmidhī (no. 2641), from az-Zubayr Ibn al ʿAwwām (raḍī Allāhu ʿanhu). It was authenticated al-Albānī in Ṣaḥīḥ Sunan al-Tirmidhī (no. 2038).