Justin Bieber & Austin Mahone -- Bury the Hatchet Over Selena ... With Basketball Game in Leather Pants

Dr. James Naismith is rolling over in his grave ... because the beloved sport he invented was desecrated in Miami yesterday when Justin Bieber and Austin Mahone put aside their Selena Gomez beef and played pick up basketball ... in LEATHER PANTS!!!

According to our sources, Bieber and Mahone got together at the Hit Factory studio in Miami thanks to YMCMB ballers Birdman and Mack Maine. The two had previously beefed over Selena Gomez ... Bieber was pissed Austin and Selena went to Disneyland together ... Mahone claimed he and Gomez were just friends.

The photos were snapped when the pair took a break from recording to play hoops (and do a little skateboarding) in the parking lot outside the studio.

We're told the two rivals hit it off so well in the studio, Justin gave Austin a song he wrote and worked with him on the vocals. JB even posted a pic with Mahone with the caption, "New music #YMCMB."