"The Messenger of Allah forbade Ad-Dubba', Al-Hantam, Al-Muzaffat, and An-Naqir, and that Al-Busr be mixed with dried dates, and that raisins be mixed with dried dates, and he wrote to the people of Hajar saying: 'Do not mix raisins and dried dates together.'"
Sunan an-Nasa'i Book 51, Hadith 18