From Sahih Bukhari (Hadith 5602):
Narrated Abu Qatada:The Prophet (ﷺ) forbade the mixing of ripe and unripe dates and also the mixing of dates and raisins (for preparing a syrup) but the syrup of each kind of fruit should be prepared separately. ( One may have such drinks as long as it is fresh)
Reference: Bukhari 5602