The believers are but a single Brotherhood: So make peace and reconciliation between your two (contending) brothers: And fear Allah that ye may receive Mercy4928 [Translation of Surah al-Hujurat (49:10) by Abdullah Yusuf Ali].
4928 - The enforcement of the Muslim Brotherhood is the greatest social ideal of Islam. On it was based the Prophet's Sermon at his last pilgrimage, and Islam cannot be completely realised until this ideal is achieved.
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Source - http://www.alim.org/library/quran/ayah/compare/49/10/allah's-commandment-to-lower-the-voice-in-the-presence-of-holy-prophet-and-make-peace-between-the-believers-if-they-fell-into-fighting-among-themselves