Yahya related to me from Malik from Zayd ibn Aslam from Ata ibnYasar that the Messenger of Allah, may Allah bless him and grant himpeace, forbade preparing nabidh from nearly ripe dates and fresh datestogether, and from dates and raisins together.
USC-MSA web (English) reference: Book 42, Hadith 7
Arabic reference: Book 42, Hadith 1546