Anas bin Sirin (may Allah have mercy on him) said: Sayyiduna Anas bin Malik (may Allah be pleased with him) sent me to collect a tenth from trade goods. Anas bin Sirin (may Allah have mercy on him) said: Collecting a tenth from trade goods is your job, and you have sent me? He said: Are you not pleased that I am sending you to the task to which Sayyiduna Umar (may Allah be pleased with him) appointed me? Sayyiduna Umar (may Allah be pleased with him) ordered me to take a quarter of a tenth from the Muslims, a twentieth from the dhimmis (protected non-Muslim subjects), and a tenth from whoever is not a dhimmi.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجزية / 18763