Ridin' on a Rainbow (1941)
Ridin' on a Rainbow is a 1941 American Western musical film directed by Lew Landers and starring Gene Autry, Smiley Burnette, and Mary Lee. Based on a story by Bradford Ropes, the film is about a singing cowboy whose investigation of a bank robbery takes him to a showboat, where he finds that a teenage singer's father has been working with the robbers to provide for her future. The film received an Academy Award nomination for best original song for "Be Honest with Me" (Gene Autry, Fred Rose).
More at Wikipedia.