O ye who believe! Let not a folk deride a folk who may be better  than they (are), not let women (deride) women who may be better than they are; neither defame one another, nor insult one another by nicknames. Bad is the name of lewdness after faith. And whoso turneth not in repentance, such are evil-doers.
Al-Qur'an (66:8)

Prophet Muhammad (peace be upon him) said: "Religion is sincerity. We said: To whom: He said: To Allah and His Book, and His Messenger, and to the leaders of the Muslims and their  common folk."
Sahih Muslim