Where did Luke get the disscussion between Agrippa and Festus found in Acts 25.?

13Now when some days had ped, Agrippa the king and Berni'ce arrived at Caesare'a to welcome Festus. 14And as they stayed there many days, Festus laid Paul's case before the king, saying, "There is a man left prisoner by Felix; 15and when I was at Jerusalem, the chief priests and the elders of the Jews gave information about him, asking for sentence against him. 16I answered them that it was not the custom of the Romans to give up any one before the accused met the accusers face to face, and had opportunity to make his defense concerning the charge laid against him. 17When therefore they came together here, I made no delay, but on the next day took my seat on the tribunal and ordered the man to be brought in. 18When the accusers stood up, they brought no charge in his case of such evils as I supposed; 19but they had certain points of dispute with him about their own superstition and about one Jesus, who was dead, but whom Paul erted to be alive. 20Being at a loss how to investigate these questions, I asked whether he wished to go to Jerusalem and be tried there regarding them. 21But when Paul had appealed to be kept in custody for the decision of the emperor, I commanded him to be held until I could send him to Caesar." 22And Agrippa said to Festus, "I should like to hear the man myself." "Tomorrow," said he, "you shall hear him."