Al-Ajlah (may Allah have mercy on him) relates from Imam al-Sha'bi (may Allah have mercy on him) that the Messenger of Allah (peace and blessings be upon him) wrote to the people of Yemen: "Zakah is only on wheat, barley, dates and raisins."
All of these hadiths are mursal, but they come through different routes, so some of them support others. Along with them is the narration of Abu Burdah from Abu Musa (may Allah be pleased with him), which has already passed in the chapter on date palms, and along with them is the statement of some of the Companions (may Allah be pleased with them).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7482