Fiqh-us-Sunnah Volume 3, Zakaat and Fasting, Fiqh 3.021A.

During the time of the Prophet, upon whom be peace, zakah was levied on wheat, barley, dates, and raisins.

Abu Burdah related from Abu Musa and Mu’azh that when the Messenger of Allah, upon whom be peace, sent the (latter two) to Yemen to teach its inhabitants Islam, he commanded them to levy sadaqah only on wheat, barley, dates, and raisins. This hadith is related by ad-Daraqutni, al-Hakim, at-abarani, and al-Baihaqi.

Commenting on the status of the report, al-Baihaqi says that its chain is muttasil (uninterrupted) and its narrators are credible.

Whether sadaqah on such items should be considered zakah or not, Ibn al-Munzhir and ibn ‘Abd al-Barr say: “The scholars are of the opinion that sadaqah is obligatory on wheat, barley, dates, and raisins.” This opinion has its roots in a saying by Ibn Majah that the Messenger, upon whom be peace, regulated the payment of zakah on wheat, barley, dates, raisins and corn. Muhammad ibn ‘Ubaidullah al-‘Arzumi, a narrator in its chain, however, is of questionable status in the eyes of the scholars, and as such, his report is not credible.