Musnad Ahmad 31:7

Mu'tamir narrated to us, he said: My father narrated to us, Abu Nadra informed us, from Abu Sa'id, he said: "The Messenger of Allah (peace and blessings of Allah be upon him) forbade the earthen jar to be used for making nabidh (fermented drink) in it. And he forbade mixing dates and unripe dates, and he forbade mixing dates and raisins together."