Hadith: A believer is not a slanderer, nor a curser, nor a person who speaks obscenely, nor a person who uses foul language

عَنْ عَبْدِ اللهِ بْنِ مَسْعُودٍ رضي الله عنه قَالَ: قَالَ رَسُولُ اللهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ:
«لَيْسَ الْمُؤْمِنُ بِالطَّعَّانِ وَلاَ اللَّعَّانِ وَلاَ الفَاحِشِ وَلاَ البَذِيءِ».
[صحيح] - [رواه الترمذي] - [سنن الترمذي: 1977]

‘Abdullāh ibn Mas‘ūd (may Allah be pleased with him) reported: The Messenger of Allah (may Allah's peace and blessings be upon him) said:
"A believer is not a slanderer, nor a curser, nor a person who speaks obscenely, nor a person who uses foul language."
[Authentic hadith] - [Narrated by At-Termedhy] - [Sunan At-Termedhy - 1977]

Explanation

The Prophet (may Allah's peace and blessings be upon him) informed us that it is not the nature of a believer who has complete Imān to criticize people’s lineage, or to revile and curse others, or to be obscene in action or speech without shame.

Benefits from the Hadith

1. The negation of Imān in the Shar‘i texts only exists due to the commission of something prohibited or the abandonment of something obligatory.
2. The Hadīth urges us to preserve our body parts and safeguard them from evil things, especially the tongue.
3. As-Sindi said: The use of slanderer and curser suggests that occasionally engaging in slander or curses, and only towards those who truly deserve it, does not detract from embodying the qualities of a true believer.