To what extent is the hadith sound that describes a handsome man appearing at the time of a person's death and entering the grave with them to defend them before Munkar and Nakir, then revealing himself to be the Qur'an that the deceased used to recite, giving them glad tidings that there will be no sorrow after this day, and preparing for them a bedding of silk and musk in Paradise?

It has been authentically reported in the Sunnah (definition) that righteous deeds, including a servant's recitation of the Qur'an, will appear as a handsome man in the grave. As narrated by Al-Bara' bin 'Azib (may Allah be pleased with him), when a believer is placed in his grave, a man with a beautiful face, clothes, and fragrance comes to him and says: "I am your righteous deed." And in the hadith (definition) of Buraydah (may Allah be pleased with him), the Qur'an will meet its companion on the Day of Resurrection as a pale man, saying to him: "I am your companion, the Qur'an." As for the hadith mentioned by the questioner, it has not been found in the reliable books of Sunnah, nor has any authentic or weak chain of narration for it been identified. It is among those things that spread on some forums and websites without investigation or verification.