Is the repentance of one who insulted the Messenger (PBUH) accepted without the Hadd punishment being carried out, and is he obligated to turn himself in if no one is aware of his crime?

The previous advice is reiterated: it is necessary to turn away from the whispers that suggest to the afflicted person that he cursed the Prophet, peace and blessings be upon him, and that this did not actually happen. In any case, whoever commits a sin must repent between himself and Allah Almighty, and is not obliged to request that the prescribed punishment be carried out on him, for the Prophet, peace and blessings be upon him, said: "Avoid these abominations that Allah Almighty has forbidden. Whoever commits any of them should conceal himself with the concealment of Allah and repent to Allah, for whoever exposes his page to us, we will apply Allah's كتاب [law/judgment] to him." This includes every sin for which repentance between the servant and his Lord suffices.