Kabshah bint Abi Maryam (may Allah be pleased with her) said: I asked Umm Salamah (may Allah be pleased with her): What things did the Prophet (peace and blessings be upon him) use to forbid? She said: "The Prophet (peace and blessings be upon him) used to forbid us from making nabidh by cooking date stones, or by mixing raisins and dates."
The Shaykh said: The prohibition of cooking date stones is emphasised because it spoils the taste of the dates, and they are the food of domestic birds and animals, and their strength is lost once they are cooked.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأشربة والحد فيها / 17461