Allah's Messenger (ﷺ) prohibited us that we should mix dry dates with unripe dates or (mix) grapes with dry dates (and prepare Nabidh). He also said: He who amongst you drinks-the rest of the hadith is the same.
Sahih Muslim Book 36, Hadith 27
← Previous Hadith He who amongst you drinks Nabidh should drink that (prepared either from) grapes alone, or from dates alone, or from unripe dates alone (and not by mixing them with one another).

Sahih Muslim Book 36, Hadith 26 Next Hadith → 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.

Sahih Muslim Book 36, Hadith 28