Not to rain on a parade, but a lot of agents simply ask on their websites for any query to include the first few pages of the manuscript.
caw
That is what the OP said.
I've seen advice both ways - send whatever the firt 5-10 pages are regardless of whether or not it's the prologue or first chapter, or only send pages from the first chapter.
The thing to consider is, does the prologue give sufficient introduction to the story you've pitched in your query. If it's in a vastly different place/time or follows characters who are not your main characters then I would recommend starting with the first chapter. When I was querying I had a seven page prologue that took place between my MC and her father she she was a child. It's important to the story for a number of reasons, but I only used it as part of my sample pages when I could include three pages of the first chapter (ten pages instead of five) because on its own the prologue seemed like a middle grade or YA book for sure.
Obviously, YMMV. Best of luck!