Tawheed

Al-Quran: O ye who believe! let not some men among you laugh at others: it may be that the (latter) are better than the (former): nor let some women laugh at others: it may be that the (latter) are better than the (former): nor defame nor be sarcastic to each other, nor call each other by (offensive) nicknames: Ill-seeming is a name connoting wickedness, (to be used of one) after he has believed: And those who do not desist are (Indeed) doing wrong*
(49 Al-Hujrat, Verse #11)