The problem[edit]
Wikipedia provides the best and most accessible single source of information on the largest number of topics in the largest number of languages. If you're anything like me, you use it all the time. If you (also like me) use Wikipedia to inform your research, teaching, or other sorts of projects that result in shared, public, or even published work, you also want to cite Wikipedia pages.
The days when teachers and professors banned students from citing Wikipedia are perhaps not entirely behind us, but let's say you're in a situation where that's not an issue. You're reading a Wikipedia page, you want to use something from it and you want to document your source responsibly. If your citation is to a piece of information that is already sourced and referenced on the Wikipedia article, you can just cut to the chase and cite that original source. But what if you want to cite the Wikpedia page itself? What can you do about the fact that any given page you cite can and probably will change?
A basic solution[edit]
A basic solution takes advantage of the fact that Wikipedia stores and makes available every previous version of every page that currently exists. In what follows below, I'll show you how you can find and cite a more durable URL (Uniform Resource Locator, or web address) that will only ever point to a specific version of a specific page. For many contexts, this is a sufficient solution, but please note that it is not comprehensive and far from "future proof" or permanent in an archival sense. Wikipedia pages can be deleted and once a page is deleted it becomes much harder to find their content again. Overcoming that requires a more advanced solution.
Anyhow, onwards with a basic, first-order fix to the immediate problem. It all starts with the little "View history" link towards the top right of every Wikipedia page...
[edit]
Let's say I want to cite the article on the Seneca Falls Convention. Here's a screenshot of that article taken in February, 2020.
1. View history for the page you want[edit]
If you click on that screenshot or navigate to any Wikipedia page (or just look at this page—even though it's not on Wikipedia it uses the same software and a very similar interface), you'll notice a little blue link near the top-right corner of the article text that says "View history." Click on that link!
2. Select the version of the page you want by timestamp[edit]
Now you should be looking at something called a "revision history" for the original page. There's a bunch of stuff, but the main thing we're interested in is the list of things going down the middle of the page. Each of the items in this list is a previous revision of the article you were looking at a moment ago. Each row corresponds to one revision and includes some useful information such as the timestamp for when the edit was saved, the username of the editor who saved it (if applicable), the length of the article in bytes after the revision (and the length of the revision in parentheses), as well as any edit summary text that the editor entered at the time they saved the revision.
Assuming the page looked okay to you when you clicked "View history" a moment ago, the version you want is the most recent one right at the top of the list (the revisions are organized in reverse chronological order by default). Go ahead and click the timestamp for this revision.
3. Use the URL with "oldid" in it[edit]
At this point, you should be looking at the article again. Indeed, if you clicked the most recent revision from the list, you are looking at exactly the same version of the article you had seen before. So what's changed? Well, for starters, the address (URL) of the page. Look at the end of it closely. It should end in "&oldid=XXXXXXXX" where the X's correspond to some numbers. This means that the address points to the specific version of the article you clicked on from the revision list. The number is called a "revision ID" and each revision ID is, in theory, unique (database errors happen, but let's just assume that's not the case because it would be a bigger issue if they started duplicating such IDs on Wikipedia...). The other difference is the little yellow box of text across the top of the page that basically explains that the address is a permanent link.
Now, finally, you have a link you can trust to point to the version of the page that is exactly as you saw it when you visited.
4. Incorporate the "oldid" URL into your preferred citation format[edit]
Once you have the oldid URL, you can go ahead and cite this URL using your preferred citation method. If your instructor, students, audience, or readers wonder why, just send them to read this page.
Are there more advanced solutions?[edit]
I called this a "basic solution", so are there others? You bet. These get more involved because they entail using another site or tool to create an archival copy of the version of the page corresponding to the revision you want to cite. One example of such a tool is perma.cc, which is what my collaborators and I use when we're citing URLs in our published work. Perma.cc is a subscription-based service that we get access to through our universities, so if that's not an option, you might also use something like the Internet Archive's Wayback Machine, where there's a little text-field where you can enter a URL to "Save page now." The Internet Archive also has browser extensions linked from their homepage if you prefer that kind of thing (I can't vouch because haven't used them myself). For most people most of the time, I suspect that these even-more-permanent archival links are not necessary. That said, at least you know about them now in case they ever become something you're looking to use!
Wait, does this mean I can cite Wikipedia for anything now?[edit]
Well, hold on there, cowboy. Wikipedia is, like any other information source, only as good as the evidence behind it. In that regard, nothing about my recommendations here make any of the information on Wikipedia any more reliable than it was before. You have to use other skills and resources to assess the quality of the information you're citing on Wikipedia (e.g., the content/quality of the references used to support the claims made in any given article). Like I said above, the problem this really tries to solve is more about how to best cite something on Wikipedia, given that you have some good reason to want to cite it in the first place.