How can we reconcile the fact that some Companions – such as Ibn Abbas – were unaware that the Hadith, "If the son of Adam had a valley of gold...," was from the Qur'an, with other narrations indicating that it is from the Qur'an?

The scholars of the Sunnah (definition) are in consensus regarding the establishment of abrogation (naskh) in the Quran and Sunnah. This abrogation is of three types: abrogation of both recitation and ruling, abrogation of recitation without the ruling, and abrogation of the ruling without recitation. It has been established that what was mentioned in the hadith (definition): "If the son of Adam had a valley full of wealth, he would desire to have another like it, and nothing fills the belly of the son of Adam except dust, and Allah accepts the repentance of whoever repents" was part of the Holy Quran, and its recitation was abrogated. This falls under the category of abrogation of recitation without the ruling. This is indicated by multiple narrations from the Companions, such as Abu Musa al-Ash'ari, Ubayy ibn Ka'b, and Aisha, where it was mentioned that it used to be recited as Quran then was removed, and that this is what used to be recited then was abrogated.