It is narrated from Sayyidah Umm Salamah (may Allah be pleased with her) that the Messenger of Allah (peace and blessings be upon him) used to forbid mixing dates with raisins, and cooking (dates) so much that their stones dissolve (and spoil).
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 20181
Kabshah bint Abi Maryam relates that she asked Sayyidah Umm Salamah (may Allah be pleased with her), the wife of the Prophet (peace and blessings be upon him), about drinks, and she said: I will tell you what the Messenger of Allah (peace and blessings be upon him) used to forbid his household: he (peace and blessings be upon him) used to forbid us from mixing raisins with dates.
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 20182