Are you looking for 100% certainty, or large general consensus? Because your title could mean both, and it will lead to very different answers.

There's an older post with some good info on this subreddit you may like to check out. https://www.reddit.com/r/AskHistorians/comments/19pgf6/what_is_the_earliest_recorded_date_that_we_can/

One of the oldest things I saw in the thread was mention of a solar eclipse recorded in stone from 3340 BC http://www.astronomy.ca/3340eclipse/ This was in Ireland.

As some kind of a follow-up question, what kind of proof do you need to be certain of the date of an event?

Would known comets be a way to date historical events? (Please don't delete this comment)

The last known inscription in Egyptian hieroglyphs was dated birthday of Osiris, year 110 of Diocletian, wich is August 24, 394 CE.

Source James P. Allen, Middle Egyptian: An Introduction to the Language and Culture of Ancient Egypt