Don't look a gift horse in the mouth.
4 seconds sound clip from the The Omega Man (1971) movie soundboard.
You can hear this line at 00:46:19 in the Blu-ray version of the movie.
Quote context
[...]
- Go' man, go! Move. Move. Wait. Get in.
- All right, you son of a bitch, just hold tight. Up against the wall, you mother.
- Now, put your hands out. Out. Way out, about shoulder high, like they're gonna crucify you, baby.
- Matter of fact, they were gonna roast me. Why'd you stop them?
- Don't look a gift horse in the mouth.
- You got any more questions, fathead?
- Down the tunnel! Down the tunnel!
- Okay, hey, hold it. Open it up.
[...]