NBA Star Isaiah Rider -- The Proof Is in My Pee

Former NBA Slam Dunk champion Isaiah "J.R." Rider claims he's been nothing less than a model parolee -- and last month, he proved it ... with his pee.

As we previously reported, Rider was arrested this week for a probation violation -- after allegedly failing to complete several probation requirements.

One of his probation officer's claims is Rider never took a required urinalysis -- a claim that has Rider p.o.'d at his P.O. ... because he actually has the receipt to prove he peed in a cup.