In the Rogue One scene in the prison cell on Jedah, Baze Malbus makes fun of Chirrut Îmwe "praying" for the cell door to open. Chirrut responds with:
Baze Malbus was once the most devoted guardian of us all.
Other than this line, do we have any evidence Baze used to be a Guardian of the Whills? It would tie in nicely with a later scene where
after Chirrut's death, he appears to regain his "faith" in the Force as he repeats his fallen friend's mantra.