Bring the receipts for, as they say

PROVE

Think of what you might do when someone doubts your story and demands evidence—it’s a short word that starts with "P."

This clue plays on the modern slang phrase "bring the receipts," which means to provide evidence or proof—often used in arguments or debates. The word "receipts" here isn’t about shopping but about backing up claims, making "prove" the perfect fit. It’s a casual way to say "show me the proof," so the answer ties directly to that idea. The "as they say" hints at the phrase’s common usage in everyday talk.