Sahih Adab al-Mufrad

It is narrated from Salim bin Abdullah, he said: I never heard Abdullah (ibn Umar) (may Allah be pleased with them) curse any person, nor anything else. Salim says that Abdullah bin Umar (may Allah be pleased with them) narrated that the Messenger of Allah (peace and blessings be upon him) said: "It is not befitting for a believer to be one who curses."

It is narrated from Sayyidah Aisha (may Allah be pleased with her) that the Jews came to the Prophet (peace and blessings be upon him) and said «السام عليكم» (may destruction be upon you). Upon this, Sayyidah Aisha (may Allah be pleased with her) said: And may destruction be upon you too, and may Allah curse you, and may Allah’s wrath be upon you. Upon this, the Prophet (peace and blessings be upon him) said: “Stop, Aisha! You should adopt gentleness, and avoid harshness and foul speech.” Aisha (may Allah be pleased with her) said: Did you not hear what they said? The Prophet (peace and blessings be upon him) said: “And did you not hear what I said? I returned it upon them. My words will be accepted against them, and their curse will not be accepted against me.”

Sayyiduna Abdullah (ibn Mas'ud) (may Allah be pleased with him) narrates from the Prophet (peace and blessings of Allah be upon him) that he said: "A believer is neither one who taunts, nor one who curses, nor one who uses obscene language, nor one who abuses."

Sayyiduna Abu Huraira (may Allah be pleased with him) narrates from the Prophet (peace and blessings of Allah be upon him) that he (peace be upon him) said: "A two-faced person is not worthy of being trustworthy."

It is narrated from Sayyiduna Abdullah (ibn Mas'ud) رضي الله عنه that he said: Among the morals of a believer, the most blameworthy is idle talk.