Is the Hadith: "It was said, 'O Messenger of Allah, what is hidden?' The Messenger said, 'That which is not mentioned,'" a Prophetic Hadith?

This is a baseless Hadith and it is not permissible to attribute it to the Prophet, peace and blessings be upon him. Al-Hafiz Al-Sakhawi, Ibn Hajar Al-Haytami, and Al-Suyuti explicitly stated its falsehood or their lack of knowledge regarding its origin. Al-Hut Al-Beiruti indicated that it is a common saying and not a prophetic Hadith. The meaning of this statement is that a servant's actions must become apparent to people. It is similar in meaning to the Hadith: "No servant conceals a secret but Allah clothes him with its garment, if it is good then it is good, and if it is evil then it is evil," except that it is more general. However, that Hadith is very weak. In conclusion, it has no basis, and the generality it implies is not supported by evidence, for a thing may remain hidden from people.