Is it permissible to phrase a supplication as, "O Allah, gladden the eyes of Your Prophet by the sight of his parents in Paradise"?

Evidence from the Sunnah (definition) indicates that the parents of the Messenger of Allah, may Allah’s prayers and peace be upon him, are in Hellfire. Muslim reported from Anas that a man said, "O Messenger of Allah, where is my father?" He said, "In the Fire." When he turned to leave, he called him back and said, "Indeed, my father and your father are in the Fire." Also, it was reported by Muslim from Abu Hurayrah, may Allah be pleased with him, that the Messenger of Allah, may Allah’s prayers and peace be upon him, said, "I asked my Lord for permission to seek forgiveness for my mother, but He did not grant it to me. And I asked Him for permission to visit her grave, and He granted it to me." Therefore, the supplication mentioned in the question is not permissible, and it is an act of transgression in supplication.