Abd Khayr said: I was near Sayyiduna Ali (may Allah be pleased with him) when the people of Najran came. I said: If he is ever going to reverse anything of Sayyiduna Umar (may Allah be pleased with him), it will be today. The narrator said: They gave greetings of peace and sat before him. Then one of them put his hand into his sleeve, took out a document and placed it in the hand of Sayyiduna Ali (may Allah be pleased with him), and they said: This is the document in your handwriting which the Messenger of Allah (peace and blessings be upon him) dictated. The narrator said: Tears flowed from the eyes of Sayyiduna Ali (may Allah be pleased with him). Then he raised his head towards them and said: This is the last document I wrote in the presence of the Prophet (peace and blessings be upon him). They said: Grant us what is in it. He said: I will soon tell you about that. Whatever Sayyiduna Umar (may Allah be pleased with him) took, he did not take for himself; he collected it for the Muslims. What Sayyiduna Umar (may Allah be pleased with him) took from you was better than what he gave you. By Allah, I will not undo anything that Sayyiduna Umar (may Allah be pleased with him) did, because Sayyiduna Umar (may Allah be pleased with him) was a man of sound judgement.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب آداب القاضي / 20376