Is one who swore by God and by the Qur’an that he had not insulted a specific person, then repeated the oath adding “nor anyone else” spontaneously, liable for lying and subject to expiation, knowing that one day he had insulted another person not intended by the oath?

Mere utterance with the tongue, without intending the meaning, is considered a vain oath (laghw al-yameen) for which there is no expiation or sin, based on the Almighty's saying: "Allah will not impose blame upon you for what is unintentional in your oaths, but He will impose blame upon you for what your hearts have earned." And reviling a Muslim without right is not permissible, based on the Prophet's (PBUH) saying: "Abusing a Muslim is فسوق (disobedience), and fighting him is disbelief," and his saying: "A believer is not a slanderer, nor a curser, nor an obscene one, nor an indecent one." Therefore, one must repent to Allah and seek forgiveness from those one has reviled without right, if possible, without incurring greater harm.