The former American footballer and movie star has been imprisoned in Nevada since 2008 on charges of kidnapping and armed robbery in relation to an armed robbery that took place at the Palace Station hotel-and-casino in Las Vegas in which sports memorabilia was taken.
After seeing his appeal for a re-trial quashed last and being informed in July 2013 he will serve at least another four years, Simpson has embraced the religion in a bid to change his life.
A source told National Enquirer magazine: ''O.J. really thought that he was going to be successful in a bid for a new trial and eventually be released from prison. ''But now he's not eligible for parole until late 2017, which has angered him.''
The disgraced 67-year-old star has become interested in the religion through his friendship with former world heavyweight boxing champion Mike Tyson, who was imprisoned in the early 1990s and is a devout Muslim.
Simpson has been studying the Koran but failed to successfully fast during the holy month of Ramadan.
An inside said: ''O.J. didn't quite make it through the entire fasting process.
''He cheated during the day, and bought snacks from the prison canteen. But he's really serious about converting to Islam. O.J. even made himself a prayer rug for his prison cell.
He really likes the idea that upon converting to Islam, all of his previous sins are forgiven. O.J. has a lot to be forgiven for.''