Brown attended a probation review hearing as part of his sentence for assaulting the 'We Found Love' singer.
"@chrisbrown I'm praying for you and wishing u the best today!" she wrote on Twitter.
"Praying for you baby, my best wishes are with you today! Remember that whatever God does in our lives, it is WELL DONE!!! #1Love."
It was revealed at the hearing that Brown had tested positive for marijuana on June 18 in Virginia, where he was doing court-ordered community service.
Rihanna was recently said to have been angered by Brown's new tattoo, which he denied depicted her beaten face.