Musnad Ahmad 32:774

Hajjaj narrated to us, Laith narrated to us, Aqil narrated to us, from Ibn Shihab, from Anas ibn Malik, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "If the son of Adam had a valley of gold, he would love to have another valley like it, and nothing fills his mouth except dust, and Allah accepts the repentance of whoever repents."