We have a letter from Muaz, from the Prophet ﷺ, stating that he took zakat only from wheat, barley, raisins (Zabib), and dates.
عندنا كتاب معاذ، عن النبي ﷺ أنه إنما أخذ الصدقة من الحنطة والشعير والزبيب والتمر.
Ahmad narrated it (21989) from Abdul-Rahman bin Mahdi, from Sufyan, from Amr bin Uthman, meaning Ibn Mawhab, from Musa bin Talha, who said (as mentioned before). As for his statement, "We have the letter of Muaz," it appears he did not hear it directly from him, but rather he transmitted it by wijadah, which is one of the methods of receiving hadith. This is why Hakim graded it sahih (1/401) and narrated it through this route, saying, "This is a hadith whose narrators have all been relied upon as proof, though the two of them (Bukhari and Muslim) did not include it. Musa bin Talha is a senior successor, and it is not denied that he could have reached the days of Muaz."This is supported by what Abu Ubayd narrated in al-Amwal (1506), where he said, "Ismail bin Ibrahim told us, from Ata bin Saaib, who said, Mughira bin Abdullah wanted to take zakat on vegetables from the land of Musa bin Talha, so Musa said to him, 'You have no right to that. The Messenger of Allah ﷺ forbade taking zakat on vegetables.'" This is a mursal report, since Musa bin Talha never met the Prophet ﷺ, but he understood from the letter of Muaz that he possessed that there was no zakat due on vegetables.Yahya bin Adam narrated it in Kitab al-Kharaj (503) from Abdul-Salam bin Harb, from Ata bin Saaib, who said, "Musa bin Mughira wanted to take from the vegetables of the land of Musa bin Talha, so Musa bin Talha said to him, 'There is nothing due on vegetables,' and he attributed this to the Messenger of Allah ﷺ." He said, "So they wrote about this to Hajjaj, and Hajjaj wrote back, 'Musa bin Talha knows better than Musa bin Mughira.'" End of quote.This contains a validation of Musa bin Talha's reliability, which is precisely what is required in a case of wijadah, for if the one who finds the document is trustworthy in his claim of having found it, his report is accepted. Furthermore, had Musa bin Talha not been confident in the authenticity of Muaz's letter, he would not have relied on it and attributed it to the Prophet ﷺ.Yahya bin Adam said in Kitab al-Kharaj (497), "As for vegetables in our usage, they include fresh herbs, aromatic plants, and greens, as well as fruits such as pears, quince, peaches, apples, figs, plums, apricots, pomegranates, cucumbers, small cucumbers, jujube, broad beans, carrots, bananas, mukl fruit, walnuts, almonds, melons, and similar produce."Malik, may Allah have mercy on him, said, "The established practice among us, on which there is no disagreement, and what I have heard from the people of knowledge, is that there is no zakat due on any of the fruits at all, such as pomegranates, peaches, figs, and similar items, nor on anything resembling them among fruits." He said, "Nor is there any zakat on cane, nor on any of the greens, nor on their monetary value when sold, until a full year has passed on their price from the day of sale, and the owner has received the payment." End of quote. See Muwatta (1/276–277).