Sahih Muslim
The Book of Drinks (Kitab Al-Ashriba)
Book Number: 023 / Hadith Number: 4904
Abu Qatada, on the authority of his father, reported Allah's Messenger (may peace be upon him) having said this: Do not prepare Nabidh by mixing nearly ripe dates and fresh dates together, and do not prepare Nabidh by mixing grapes and dates together, but prepare Nabidh from each (one of them) separately.