Justin Bieber Asked Stephen Baldwin for Hailey's Hand in Marriage

Justin Bieber's a sucker for old school traditions -- he made sure to ask Hailey Baldwin's father for her hand in marriage before he popped the question ... TMZ has learned.

Sources close to the couple tell us Justin and Stephen Baldwin met face-to-face several weeks ago. We're told the conversation was very important to the Biebs, who absolutely wanted the green light from Hailey's pop. Stephen is a minister in NY, and we're told he believes Justin has the same Christian values as he and Hailey do -- and, of course, JB and HB both attend Hillsong Church.

Point is ... Stephen happily gave his blessing. The mano a mano also proves Justin's proposal wasn't an impulsive decision in the middle of a vacation.

We broke the story ... Justin proposed to Hailey Saturday at a resort in the Bahamas. Hailey, obviously, said yes ... and was flashing her engagement ring all day Sunday.

Justin referenced those Christian values that so impressed his father-in-law-to-be when he posted an open love letter to Hailey. The super romantic message was really his first public declaration about Hailey since they reunited.

It's interesting, Justin got the go-ahead from Stephen sometime in June, and, as we've seen, the couple's been inseparable since their PDA-filled Miami weekend on June 10.