Is swearing very bad in Islam?

Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

Swearing is considered a debauchery and an immoral act.

Bukhari and Muslim reported that Ibn Massaoud narrated that the Prophet (Sallallahu Alaihi wa Sallam) said: “Swearing to a Muslim is a debauchery and an immoral act, and killing a Muslim is an act of Kufr.”  Such behaviour (swearing) contradicts the complete Iman of the person who does it.  Imam Ahmad and Tirmizi reported that Ibn Masoud narrated that the Prophet (Sallallahu Alaihi wa Sallam) said: “A Muslim is not a person who slanders, curses, speaks obscene words or is abusive.”  Bukhari also reported that Abdullah Bin Omar narrated that the Prophet (Sallallahu Alaihi wa Sallam) said: “A Muslim is a person whom all Muslims are safe from his tongue and hands.”

In a long Hadith reported by Tirmizi, Ahmed, and Ibn Majah; Mu’adh narrated that "The Prophet (Sallallahu Alaihi wa Sallam) mentioned to him what brings him closer to Paradise and what makes him be farther from the Hellfire, and then he told him: “Shall I not inform you of what controls all that.”  Mu’adh said: “Please tell me O! Prophet of Allah (Sallallahu Alaihi wa Sallam)”.  So the Prophet (Sallallahu Alaihi wa Sallam) took his tongue (with his fingers) and told him: “Restraint this one.”  Then Mu’adh said: “O! Prophet of Allah (Sallallahu Alaihi wa Sallam), are we held accountable for what we say.”

The Prophet (Sallallahu Alaihi wa Sallam) said: “How are you asking this question?”  People are not thrown into the Hellfire on their faces or noses except due to the result of their tongues.”