Musannaf Ibn Abi Shayba 36:499

'Abd al-A'la and Ibn Mubarak narrated to us, from Ma'mar, from al-Zuhri, from Sa'id ibn al-Musayyib: That 'Ali sought from the Prophet—may Allah honor him—what is sought from the deceased, but he did not find anything. So he said: "My father and my mother be sacrificed for you; you were pure in life and you are pure in death."