What is the ruling on one who has lost trust in Allah? And what is incumbent upon him to do?

What the speaker uttered is a great reprehensible statement, and he must hasten to sincere repentance and harbor good thoughts about his Lord; for Allah's decree is between grace, justice, mercy, and wisdom, and His choice is better than a servant's choice for himself. Indeed, ill thoughts about Allah and despairing of His spirit are among the major sins. Ibn Hajar said: "The forty-first and forty-second major sins are: ill thoughts about Allah the Almighty and despairing of His mercy." Allah the Almighty said: "And who despairs of the mercy of his Lord except the misguided?" Ill thoughts about Allah may contradict the very essence of monotheism; for Allah has singled out the disbelievers for despairing of His mercy, and He has threatened them with a painful torment, as Allah the Almighty said: "Indeed, no one despairs of relief from Allah except the disbelieving people." Ill thoughts may eventually lead to disbelief. And good thoughts about Allah are among the obligations of monotheism, while ill thoughts contradict it; for Allah described the hypocrites as harboring untrue thoughts about Him. Therefore, this person must sincerely repent, harbor good thoughts about his Lord, be assured of His promise, submit to His judgment, and be content with His decree and destiny.