What is the fatwa regarding the oath: "It is unlawful for me if I said that," when it became clear that the speaker did say it?

It is not permissible for a Muslim to swear by anyone other than Allah. Whoever swears by other than Allah has committed shirk (polytheism), for the Prophet, peace and blessings be upon him, said: "Whoever takes an oath should swear by Allah or remain silent," and "Whoever swears by other than Allah has committed shirk." If an unlawful oath is taken without a specific intention, the ruling is that it incurs the expiation for ẓihār (a type of divorce pronouncement) for a married man, and the expiation for an oath for an unmarried man. As for swearing unknowingly (due to forgetfulness), there is no expiation required of you, according to the majority of scholars. However, you are obligated to repent and seek forgiveness for swearing by other than Allah, for the Prophet, peace and blessings be upon him, said: "Indeed, Allah has forgiven my ummah (nation) for their mistakes, forgetfulness, and what they are coerced into."