Musnad Ahmad 32:1642

Qutaybah ibn Sa'id narrated to us, Rashdin ibn Sa'd narrated to us, from Qurrah, and 'Aqil, and Yunus, from Ibn Shihab, from Anas ibn Malik, that the Prophet, may Allah bless him and grant him peace, said: "If the son of Adam had a valley of gold, he would seek another valley with it, and nothing will fill his mouth except dust, then Allah turns in forgiveness to whoever repents."