Sahih Bukhari Volume 7, Book 74, Hadith 5604

حَدَّثَنَا مُسْلِمٌ، حَدَّثَنَا هِشَامٌ، أَخْبَرَنَا يَحْيَى بْنُ أَبِي كَثِيرٍ، عَنْ عَبْدِ اللَّهِ بْنِ أَبِي قَتَادَةَ، عَنْ أَبِيهِ، قَالَ نَهَى النَّبِيُّ صلى الله عليه وسلم أَنْ يُجْمَعَ بَيْنَ التَّمْرِ وَالزَّهْوِ، وَالتَّمْرِ وَالزَّبِيبِ، وَلْيُنْبَذْ كُلُّ وَاحِدٍ مِنْهُمَا عَلَى حِدَةٍ‏.‏

Narrated By Abu Qatada : The Prophet 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).