"The Messenger of Allah forbade mixing Al-Busr with dried dates, or raisins with dried dates, or raisins with Al-Busr, and he said: 'Whoever among you (wants to) drink them, let him drink each one of them on its own: dried dates on their own, or Al-Busr on their own, or raisins on their own."
Sunan an-Nasa'i Book 51, Hadith 30