A most notable story on justice with Umar ibn al-Khattab, Sa'd ibn Abi Waqqas, and Anushirvan

I have heard the following narration (I summarized it, and some parts may be paraphrased) > While Sa'd ibn Abi Waqqas was the governor of Damascus at the time of > Umar ibn al-Khattab, he wanted to extend a mosque in Damascus. So > he bought the lands around the mosque. A Jewish man, however, refused to > sell his property. Finally, Sa'd ibn Abi Waqqas simply took the > ownership of the land and had his men pay the Jewish man. There was > nothing the Jewish man could do. One day, he told what happened to his > Muslim neighbor. The neighbor told him to go to Medina, and find caliph > Umar: “I am told that he is a most just ruler.” > > So the man goes to Medina, asks about Umar when he gets there, people > point at a man under a tree. He goes to the man, introduces himself, > and narrates what happened. Umar writes a note, and tells the man to > give it to the governor of Damascus. The note says: **I am not any less > just than Anushirvan .** The man looks at Umar, looks at the note, > thanks him and leaves. > > When he arrives at Damascus, he is hesitant about what to do. A > modest man gave him a one-line note which would hardly change > anything. Still, he invested a lot in this matter already, so he goes > to the governor, says he has seen caliph Umar, and gives him the note > that Umar gave. As soon as he reads the note the governor's face pales, > his hands starts to shake. He says: “consider your land is given to > you.” > > The man so surprised that his curiosity about > what the hell is happening overwhelms his joy of having his land back. > He begs the governor: “Please, just tell how this note made change your > mind in an instant!” > > The governor says, here is why. Before Islam, Umar and I went to Persia for trade. While we were in > Persia, a group of gangsters came and took our camels and our money. > There was nothing we could do; there were too many of them. Back at the > inn we were staying, we told what happened to the inn-keeper. The > inn-keeper told us to go to King Anushirvan, that he was a most just > king. So we went to the king. We were given a translator. We told out > story to the translator, the translator narrated the story to the > king. The king ordered that we should each be given a bag of gold. > Back at the inn, we told the inn-keeper what happened. The inn-keeper > was slightly puzzled. He said there must be some misunderstanding: > “Come, tomorrow we go together, and this time I will be your > translator.” > > Next day, the three go to the King again. The inn-keeper narrates what > happened. The King's face pales. He orders that two bag of golds shall > be given to each of us, and our camels also. The king added: “when you > are leaving the city, one you shall leave from the East entrance and > the other from the West entrance.” > > We were of course most puzzled. Back at the inn, the inn-keeper told > us the story. He said, when we narrated him what happened, he realized > that gang was the gang of the king's son, and the king's second > man. When he narrated the story to the king, he of course realized who > was who. > > When I was leaving the city I saw to men hanged. There was a big crowd > around them. I asked about them and someone said, these two are the > son and the second man of the king, they robbed traders. There was > another man hanged at the other entrance, he was the translator, who > mistranslated our story so as to protect them. The king ordered the > execution of his own son! > > Now you see what Umar means with his note. He is telling me that he will > execute me just like the king executed his son. > > Upon hearing all this, the Jewish guy not only granted his land, but > he also became a Muslim. What is the strongest source of this narration?