All believers are but brethren. Hence, [whenever they are at odds,] make peace between your two brethren, and remain conscious of God, so that you might be graced with His mercy.
Al-Hujurat (The Dwellings) Verse 10
The Prophet said, "The most hated person in the sight of Allah is the most quarrelsome person."
Sahih Bukhari: Volume 3, Book 43, Number 637