Ziyad bin Hudayr said: I used to collect the tithe from Banu Taghlib whenever they came and went. An old man of theirs went to Sayyiduna Umar (may Allah be pleased with him) and said: Ziyad collects the tithe from us twice.
Sayyiduna Umar (may Allah be pleased with him) said: This will suffice you. Then the old man came to Sayyiduna Umar (may Allah be pleased with him) again, while Sayyiduna Umar (may Allah be pleased with him) was in a gathering, and said: O Commander of the Believers, I am a Christian shaykh. Sayyiduna Umar (may Allah be pleased with him) said: And I am a hanif shaykh (that is, one devoted solely to the One Allah). It will suffice you. The narrator said: Then he wrote to me that I should collect the tenth from them only once a year.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجزية / 18774
Ruzayq bin Hayyan said: Sayyiduna Umar bin Abd al-Aziz (may Allah have mercy on him) wrote to me that I should collect from the dhimmi traders a twentieth of those goods, and if it is less, then in the same proportion, until it comes down to ten dinars. If it falls short by a third of a dinar, then collect nothing, and whatever you collect, record it in writing for the year.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجزية / 18775