Musannaf Ibn Abi Shayba 35:140

Muhammad ibn Bishr narrated to us, from Hajjaj ibn Abi Uthman, from Yahya ibn Abi Kathir, from Abdullah ibn Abi Qatadah, from his father, from the Prophet (peace and blessings of Allah be upon him), who said: "Do not make nabidh (a fermented drink) from dates and raisins together, and do not make nabidh from unripe dates (zahw) and ripe dates (rutab) together. Rather, make nabidh from each one of them separately."