It is narrated from Hazrat Abu Saeed (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) forbade making and using nabidh in earthen pots, and also forbade making nabidh by mixing unripe and ripe dates, or by mixing dates and raisins.
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 10991