Musnad Ahmad 1103:1

Hassan ibn Musa narrated to us, Ibn Lahi'ah narrated to us, Bukayr ibn al-Ashajj narrated to us, from Yusuf ibn Abdullah ibn Salam, that he said: The Messenger of Allah, peace and blessings of Allah be upon him, was asked: "Are we in a state of goodness, or are those who come after us?" The Messenger of Allah, peace and blessings of Allah be upon him, said: "If one of them were to spend the equivalent of Mount Uhud in gold, it would not reach the mudd of one of you, nor half of it."