[The ruling on one who frequently curses and uses obscene speech while he is committed to acts of obedience]

The answer: In some societies, a man may grow up, and cursing and obscene speech enter into his language and his speech as a consequence of the language and speech of his community. Then he grows older, turns to Allah, and becomes committed to obedience to Him. Yet still, there issues from him what issues of cursing and insulting, without intention or purpose towards the meaning. Rather, what issues from his tongue issues only because of the language upon which he grew up, and it became his nature and disposition.
Such a person ought not to be judged as being in a state of disobedience and sin. And Allah, exalted is He, has said concerning something of this type, according to one of the two interpretations: "Allah does not call you to account for what is idle in your oaths, but He calls you to account for what your hearts have earned. And Allah is All-Forgiving, All-Forbearing." [al-Baqarah:225]
However, whoever is in such a state ought to train his tongue to leave off cursing and obscene speech. I myself have seen and heard many of this sort, in whose speech there runs much cursing and insulting, without any intention on their part towards its meaning.
If you were to say to one of them, “Why do you insult and curse?” he would deny that, and that is only because insulting and cursing have entered into their language.
At the same time, they use cursing and insulting as a metaphor for something else. So they say, “The cold ‘had intercourse with’ him,” meaning: the cold hurt him severely. And they say, “So-and-so ‘had intercourse with him’ in his merchandise,” when he bought it from him and overpowered him in the purchase. And, “He ‘had intercourse with him’ in his right,” meaning: he bought it from him, or overpowered him in it by a judgement, or by purchase, or the like of that. And, “He ‘had intercourse with him’ with a stab,” that is, he stabbed him with a thrust. And, “I will curse his face,” meaning: I will humiliate him.
And we have heard them inserting insulting expressions into the speech of a friend with his friend, and a brother with his brother, without intending by it the meaning of insult, nor desiring it. Rather, it is of the same kind as what has come in the ḥadīth: “Then marry the one who is religious – may your hands be dusty.” The phrase “may your hands be dusty” is a supplication for destruction, but it is not intended in the ḥadīth nor meant; rather, it entered into the ḥadīth following the (customary) language.
And likewise the expression “Woe to his mother,” which is (literally) a supplication against him for destruction, and yet the Messenger of Allah (May Allah bless him and his family and grant them peace) said it concerning some of his allies among the believing fighters in the path of Allah.

Source: Min Thimār al-ʿIlm wa al-Ḥikmah vol.2