Is saying "Haram upon You, O Allah" in a moment of anger and despair, then immediately seeking forgiveness, considered an exit from the fold of Islam, and what must the speaker do to repent?

Panic and ill-mannered behavior towards Allah in times of calamity stem from weak faith and lack of patience. Allah Almighty commanded patience and gave glad tidings to the patient, who say, "Indeed we belong to Allah, and indeed to Him we will return," when afflicted. Allah is not questioned about what He does, and He is the Owner of sovereignty. If you utter a bad phrase in a state of extreme anger without intention, then Allah is too generous to hold you accountable, as He says: "Our Lord, do not impose blame upon us if we have forgotten or erred." The Lawgiver has excused unintentional utterances from the sleeping, the forgetful, the intoxicated, the ignorant, the coerced, and those who err due to extreme joy or anger.