Rivers said Jackson will join the team Tuesday in Boston.
Jackson tweeted Sunday evening:
I never lost faith. The wait is over. http://t.co/kXmH7S7mR1— IG: stak5ots (@DaTrillStak5) December 9, 2013
He also posted to his Instagram on Monday, "One thing about me I never panic bkuz God taught me how to enjoy the bad and good times. It's easy to b positive when u are thankful and humble. God is Great. Let's turn up LA. Promise to give my all."
Jackson spent last season with the Spurs, but was waived shortly before the postseason because of an apparent dust-up with the coaching staff after being unwilling to accept a lesser role behind Kawhi Leonard and Danny Green.
Jackson, 35, averaged six points and three assists last year for San Antonio on 37 percent shooting from the field.