Ibn Mas‘ūd (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) said: "There is nothing heavier on the scale than good manners. Indeed, Allah detests the one who is indecent and foulmouthed."
Abu Ad-Dardā' (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) said: "A believer is neither a slanderer or an invoker of curse, nor is he indecent or foulmouthed."
The first Hadīth encourages good manners, such as refraining from harming others while lending them support and a cheerful face. These deeds are the heaviest on one's scale on the Day of Resurrection. Also, Allah, the Almighty hates the person who is indecent and foulmouthed. The second Hadīth states that a perfect believer does not find fault with others or disparages them, nor does he insult or curse them frequently. He does not defame their lineage or honor, nor does he criticize their appearances and hopes. Instead, strong faith impels one to adopt noble manners and avoid bad ones.