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