Just remember: Don’t ask where to download it. Do ask how to dump it.
If you have a BIOS file, check its hash. If it matches, you’re good. If not, delete it and find a clean dump. A common question: “Does region matter for emulation?”
Many modern emulators (especially DuckStation and later Beetle PSX) can actually run many games a BIOS via “HLE” (High-Level Emulation). But you’ll lose the boot logos, and some games (especially those with custom CD audio or anti-piracy checks) can glitch out.
The only legal method is to dump it from your own, physical PlayStation console.