This is the single most useful thing to understand about language models: they predict plausible text, they don't look facts up. A source that sounds right can be pure invention. You can't switch it off completely, but you can reduce it a lot.

• Bring the facts yourself. Paste the report, article or data into the prompt, and tell it: "Answer only from the text below. If something isn't there, say 'not in the provided text'."
• Ask it to quote. "Give the exact sentence you're relying on for each number." If it can't, you've found a guess.
• Don't ask it to produce statistics from memory. Ask what to search for instead, then find the number yourself.
• Label confidence. "Mark each claim as [from my text], [general knowledge] or [unsure]."
• Verify anything that matters. Numbers, names, links and quotes get checked by a person, every time.

So in practice it's both: phrase the request to give it less room to invent, and still double check what you're going to publish.