The older the better, but it doesn't have to be the oldest you can think of, especially if it's more interesting to talk about something more recent. Nevertheless, older is generally more interesting from the point of view that I'm interested in right now, which is the one that wants to know more about the nature of Propaganda.
Probably the account of the Battle of Kadesh as told by the Egyptians in 1274 BC. The battle led to what may have been the first recorded peace treaty in history, but both sides have claimed victory in their own accounts. The Egyptian account says that Ramesses II himself, drawing strength from the god Set, personally slew the top command for the Hittites and say that their wretched, vanquished leader, Muwatalli, pleaded with Ramesses II thusly:
Suteh are you, Baal himself, your anger burns like fire in the land of Hatti... Your servant speaks to you and announces that you are the son of Re. He put all the lands into your hand, united as one. The land of Kemi, the land of Hatti, are at your service. They are under your feet. Re, your exalted father, gave them to you so you would rule us. Is it good, that you should kill your servants? ... Look at what you have done yesterday. You have slaughtered thousands of your servants ... You will not leave any inheritance. Do not rob yourself of your property, powerful king, glorious in battle, give us breath in our nostrils.
Whereas in reality Kadesh was not captured by the Egyptians, and the battle is mostly viewed as a draw by modern historians, which is what led to the peace treaty.
http://www.reshafim.org.il/ad/egypt/ramseskadeshcampaign.htm