Sayyiduna Abu Musa and Sayyiduna Mu'adh bin Jabal (may Allah be pleased with them both) relate that the Messenger of Allah (peace and blessings be upon him) sent the two of them to Yemen and commanded them to teach the people the rulings of their religion, and said: "Do not take zakah from anything except these four kinds; the four kinds are: barley, wheat, raisins and dates."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7451
Abu Musa al-Ash'ari and Mu'adh (may Allah be pleased with them both) say that when the two of them were sent to Yemen, they did not take zakah except from wheat, barley, dates and raisins.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7452
Bishr bin Asim and Uthman bin Abdullah bin Aws (may Allah have mercy on them both) say that Sufyan bin Abdullah al-Thaqafi (may Allah be pleased with him), who was his governor over Ta'if, wrote to Sayyiduna Umar (may Allah be pleased with him). He wrote that in his area there were orchards containing grapevines, and containing peaches and pomegranates whose yield is many times greater than that of the grapevines; and he wrote seeking his instruction regarding the tithe ('ushr) on them. Sayyiduna Umar (may Allah be pleased with him) wrote back to him that there is no tithe on them, because they are all among the thorny shrubs ('idah), so there is no tithe on them.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7454