That's one of Tim Tebow's commandments -- and it led to an incredible moment during his run with the NY Jets, when Tim refused to call a play called an "Oh Sh*t Screen."

Tim's former Jets teammate, Nick Mangold, told the story about a moment during the 2012 season on BroBible's "Endless Hustle" podcast ... and it's pretty hilarious!!

"We had a play that was a 'Y Oh Sh*t' screen, where the tight end actually fakes like he fell down on a running play, hops up, runs back over, throws back to the tight end and it's usually wide open," Mangold said.

But Tim -- who's never committed a single sin in his life --  refused to drop the s-bomb while calling the play in the huddle.

"He goes through the whole formation and gets to the last play: 'Y, Alright Screen' ... you guys know what it is.'"

"And we’re like, 'No Tim, what is it?' ... then he goes, 'No, I’m not going to say it.'"

Seems the whole team jokingly tried like hell to coax Tebow into saying the word -- but he stayed strong and refused to let the expletive fly.

The way Mangold tells the story ... it was all in good fun, but Tebow never wavered!

In the end, Mangold said the team got in trouble for taking too long in the huddle.