Members of a rap group founded by Tupac Shakur have released a new video in which they claim they rolled up Pac's ashes with marijuana and SMOKED him after he passed away.

The Outlawz -- most famous for the Biggie Smalls diss track "Hit 'em Up" -- said, "Yeah, it's definitely true" ... claiming it all went down at a beach memorial for Pac -- and his mom was present at the time.

The rappers claim the idea was inspired by a lyric in one of Tupac's songs in which he said, "Last wishes n**gas, smoke my ashes."

So ... the Outlawz say they simply followed Pac's request -- explaining, "We twist up some of that great-granddaddy California kush ...and mixed the big homie with it ... so you know, [Tupac is] flowin' through our system."