To what extent is the hadith: "If the son of Adam had a valley full of gold, he would wish for another like it, and nothing will fill the belly of the son of Adam except dust, and Allah turns in forgiveness to whoever repents," authentic, and is this hadith considered a verse from the Book of Allah that was not written down?

The hadith contains a clear textual distortion or typographical error, and it was narrated correctly by Al-Suyuti and Al-San'ani.

The hadith was reported in Sahih Muslim and Al-Bukhari, and it was also cited by Ahmad and Ibn Hibban in his Sahih from another chain of narration on the authority of Ibn Abbas.

There is a problem and a contradiction between the narrations of the hadith from Ibn Abbas and Ubayy. Al-Bukhari narrated it from Ibn Abbas with the wording: "If the son of Adam had two valleys of wealth, he would desire a third, and nothing will fill the belly of the son of Adam except dust, and Allah accepts the repentance of whoever repents." Ibn Abbas mentioned that he did not know whether it was from the Quran or not.

Al-Bukhari also narrated from Anas, on the authority of Ubayy, that they used to consider this from the Quran until Surat At-Takathur was revealed.

Al-Hafiz Ibn Hajar said: "It was a Quranic verse, then its recitation was abrogated when Surat At-Takathur was revealed, but its ruling remained in effect."

It is possible that the Prophet, peace and blessings be upon him, informed about it from Allah Almighty as part of the Quran, or that it is from the Hadith Qudsi. If it was from the Quran, then it is among what had its recitation abrogated.