The other offences of the tongue, in addition to them being types of oppression (which itself, according to reason and religion, is forbidden), have also been prohibited in Islamic sources under their very names. Some examples are given below:
Allah the Most High said: “O you who believe, let not (one) people laugh at (another) people, perchance they may be better than they, nor let women (laugh) at (other) women, perchance they may be better than they; and do not find fault with other people, nor call one another by nicknames; evil is a bad name after faith, and whoever does not repent, he it is who is unjust.”
The Holy Prophet Mohammad (pbuh&hh) said: “Anyone who makes light of a poor believing Muslim, he has made light of Allah Himself, and Allah will make light of him on the Day of Resurrection if he does not repent. Anyone who respects a poor believing Muslim, he will meet Allah on the Day of Resurrection while He is pleased with him. Indeed anyone who respects his believing Muslim brother, he respects Allah the Almighty.”
He (pbuh&hh) also said: “Anyone who abases a poor believing Muslim for his poverty and makes light of him, he has made light of Allah and remains in the wrath of Allah until he goes to one whom he has wronged and apologizes to him and the other becomes pleased with him.”
He (pbuh&hh) also said: “Allah said: ‘Anyone who abases my believing servant, he has declared war against Me’.”
He (pbuh&hh) also said: “Anyone who annoys a believer, Allah annoys him; and anyone who saddens a believer, Allah will bring sadness to him.”
He (pbuh&hh) also said: “Anyone who glares at a believer with a look to frighten him, Allah will frighten him on the Day when there is no shelter except His own.”
He (pbuh&hh) also said: “The entire being of a believer is a sanctuary that is his prestige, his property and his life.”
He (pbuh&hh) also said: “Insulting a believer is a great transgression and fighting him is unbelief, eating his flesh (backbiting him) is a sin, and respecting his property is like respecting his life.”
He (pbuh&hh) also said: “Anyone who rebukes the slightest fault of a believer will not die until he himself commits that fault.”
Imam Mohammad al-Baqir (a.s.) said: “Beware of being snide to the believers.”
He (a.s.) also said: “There is no one who is snide in the presence of a believer except that he dies with the worst kind of death, and wilt not be given the grace to be on the path of accomplishing good actions.”
Imam Ja’far al-Sadiq (a.s.) said: “Do not disregard a poor believing Muslim; because anyone who disregards or makes light of him will he disregarded by Allah.”
He (a.s.) also said: “Anyone who disregards a believer whether poor or not, Allah disregards him until he ceases his action.”
He (a.s.) also said: “Allah has said: ‘Let anyone who annoys My believing servant announce a war against Me, and let anyone who respects My believing servant be safe from My anger.’”
Imam Ja’far al-Sadiq (a.s.) said: “Surely cursing when uttered by the cursor moves back and forth between him and the person cursed. If it finds any reason to be attached to the victim, it attaches; but if not, the curser himself becomes worthy of it, and it comes back to him. Therefore beware of cursing a believer, lest your curse come back to you.”
He (a.s.) also said: “Anyone who rebukes a believer, Allah the Almighty will rebuke him in this world and the hereafter.”
He (a.s.) also said: “He is cursed, he is cursed, he who attributes unbelief to a believer, and he who attributes unbelief to a believer is like his murderer.”
source:english.almaaref