Sayyiduna Attab bin Asid (may Allah be pleased with him) said that the Messenger of Allah (peace and blessings be upon him) used to send assessors to estimate their grapes and fruits.
In a narration of Imam al-Shafi'i (may Allah have mercy on him): He (peace and blessings be upon him) used to send those who would estimate the people's grapes and fruits.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7431
Sayyiduna Attab bin Asid (may Allah be pleased with him) said that the Messenger of Allah (peace and blessings be upon him) said: "Grapes are to be estimated just as dates are estimated, and their zakah is to be taken in raisins, just as the zakah of dates is taken."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7432
Sa'id bin al-Musayyib (may Allah have mercy on him) said that the Messenger of Allah (peace and blessings be upon him) ordered Attab bin Asid (may Allah be pleased with him) to estimate grapes just as dates are estimated. Then he said: "Pay its zakah in raisins, just as the zakah of dates is paid in dried dates." He said: This is the Sunnah of the Messenger of Allah (peace and blessings be upon him) concerning dates and grapes.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7434
Sayyiduna Abu Umamah bin Sahl (may Allah be pleased with him) stated in the gathering of Sa'id bin al-Musayyib (may Allah have mercy on him) that the Sunnah has been established that zakah is not to be collected from dates and grapes until their estimate reaches five wasq. Al-Zuhri (may Allah have mercy on him) said: I have not known any produce to be estimated except dates and grapes.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7435