Using copyright beats for mixtape?

I'm planning to do a mixtape using other rapper's beats. I'm NOT going to SELL OR RELEASE the songs to radio, stores, itunes or performance, etc. I'm only go to release them to a FREE mixtape. I tried researching info so I won't get sued but I get BOTH answers. I get "yes you can use them as long as they're not for profit" "no you can't use them because it's illegal" SO I'M CONFUSED! PLEASE give me the REAL answer. Be detailed on this you guys! I see a lot of rappers doing mixtape like Nicki Minaj using "She gotta donk" for "Itty Bitty Piggy". So I'm CONFUSED