"The Messenger of Allah forbade us to soak two things together when one is more potent than the other. I asked him about Fadikh (a drink made from fresh dates cut open) and he forbade it. He disliked the extra bit on Al-Busr, fearing that that might make it two things, so we used to cut it off."
Sunan an-Nasa'i Book 51, Hadith 24