It is narrated from a man of Thaqif: Sayyiduna Ali (may Allah be pleased with him) appointed me as governor over Buzurj Sabur and said: "Do not strike any man with a whip in collecting a dirham, do not sell their provisions or their winter and summer clothing, nor the animal on which they do their work, and do not make any man stand (harshly) in order to collect a dirham." The narrator says: I said: "O Commander of the Faithful! Then I will return to you just as I am leaving you." The Commander of the Faithful (may Allah be pleased with him) said: "Even if you return just as you went, woe to you! We have been commanded only to take the surplus from them."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجزية / 18736