TMZ obtained video from Justin's Saturday tour stop in Miami, where he told a packed house at the Kaseya Center to "be careful out there" -- this after chit-chatting with the audience and asking if there were any singles in the building, playfully noting "the night is young."

Check it out ... JT was in jovial mood this past weekend while performing in the Magic City -- bantering with the crowd and eventually noting he'd have to be asking for forgiveness the next day (Sunday) ... which just so happened to be Father's Day.

It's a little unclear what he was getting at -- but from the sounds of it, he was kidding about enjoying Saturday night ... and heading to church on Sunday to repent for misdeed, something most can relate to.

The crowd seemed to get the joke and laughed it up with him ... and that's when he started asking around about people who were flying solo at his show -- going on to crack jokes with them as well, which is when his light-hearted warning was uttered.

Of course, a little over 48 hours later early on Tuesday morning ... Justin found himself being busted by cops in the Hamptons for allegedly driving while intoxicated. So, it doesn't look like JT followed his own advice ... 'cause he did end up running into trouble.

As we reported ... the *NSYNC alum was pulled over by police after they claimed he blew through a stop sign and was seen swerving on the road.

Justin allegedly told police he only had one drink and was following friends home from dinner at a swanky hotel ... though cops say he reeked of booze and had bloodshot eyes, slurred speech, etc.

The singer's lawyer, Edward Burke Jr., says he's going to vigorously fight the charges ... and Justin's planning to continue his world tour Friday and Saturday at the United Center in Chicago.

It will be interesting to see what he has to tell the crowd then about this ... if anything at all.