In a handwritten note posted to Instagram, WNBA star Brittney Griner thanked supporters for writing to her while she was imprisoned in Russia and urged them to do the same for Paul Whelan, an American who remains incarcerated in the country.

Griner, who was released from custody after U.S. and Russian officials agreed on a prisoner swap earlier this month, said Wednesday that the letters she received during her 10-month imprisonment helped her stay optimistic throughout the ordeal.

Your letters helped me to not lose hope during a time where I was full of regret and vulnerable in ways I could have never imagined. Thank you, from the bottom of my heart. Because of you I never lost hope, she wrote.