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كتاب الأشربة
74  
Drinks
(11)
Chapter: Unripe-date drink and ripe-date drink should not be mixed if it is an intoxicant, and two cooked foods should not be put in one dish
(11)
باب مَنْ رَأَى أَنْ لاَ يَخْلِطَ الْبُسْرَ وَالتَّمْرَ إِذَا كَانَ مُسْكِرًا وَأَنْ لاَ يَجْعَلَ إِدَامَيْنِ فِي إِدَامٍ
Sahih al-Bukhari 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 )

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.‏
Reference : Sahih al-Bukhari 5602
In-book reference : Book 74, Hadith 28
USC-MSA web (English) reference : Vol. 7, Book 69, Hadith 507
  (deprecated numbering scheme)