What should a young man who has repented sincerely do to rid himself of pangs of conscience, after he took money from his maternal uncle without his knowledge when he was young, and now he cannot return the money or tell his uncle due to his financial circumstances and his good reputation within the family?

You must return any money to its owners, as Imam Ahmad narrated that the Messenger of Allah (peace be upon him) said: "The hand is responsible for what it takes until it returns it." Al-Bukhari narrated: "Whoever has wronged another concerning his honor or anything else, let him seek his forgiveness today before there are no dinars or dirhams. If he has good deeds, they will be taken from him proportionate to his wrongdoing. If he has no good deeds, then some of the wronged person's sins will be taken and placed upon him." It is not necessary to inform the owner of the money about what happened; it is sufficient to return it to him in any possible way that preserves your dignity. If you cannot return it now, it remains a debt upon you until you are able to, according to the verse: "And if there is one in adversity, then [let there be] a postponement until a time of ease." It is recommended to conceal one's own faults, as the Messenger of Allah (peace be upon him) said: "Whoever commits any of these abominations, let him conceal himself with the concealment of Allah." You can document the amount in writing or with witnesses to guarantee the right of the owner of the money without mentioning the reason. If you fear death and cannot return the money, do not hesitate to ask the owner for forgiveness or a grace period, as the rights of people are not waived except by fulfilling them or by the owners forgiving them. As for your prayers and good deeds, they are valid, and you are not required to repeat them as long as they were performed according to their conditions. This is the opinion of the majority of scholars.