Probably the easiest way to solve this problem in the future is to know that the same account posts it each month, so you can just check that account's submissions: <a href="https://news.ycombinator.com/submitted?id=whoishiring" rel="nofollow">https://news.ycombinator.com/submitted?id=whoishiring</a>
For future reference, an easy way to search for the post is to search "Who is hiring" and then sort the results by Date instead of Popularity and you should be able to find it pretty easily.