Al-Hujurat 49:11 يا ايها الذين امنوا لا يسخر قوم من قوم عسى ان يكونوا خيرا منهم ولا نساء من نساء عسى ان يكن خيرا منهن ولا تلمزوا انفسكم ولا تنابزوا بالالقاب بيس الاسم الفسوق بعد الايمان ومن لم يتب فاولايك هم الظالمون ١١

O you who believe! Let not a group scoff at another group, it may be that the latter are better than the former. Nor let (some) women scoff at other women, it may be that the latter are better than the former. Nor defame one another, nor insult one another by nicknames. How bad is it to insult one’s brother after having Faith [i.e. to call your Muslim brother (a faithful believer) as: "O sinner", or "O wicked"]. And whosoever does not repent, then such are indeed Zâlimûn (wrong-doers, etc.).