The Rounders (movie, 1965)

Ben (Glenn Ford) and Marion (Henry Fonda) are two cowboys who make a meager living breaking wild horses. Their frequent employer Jim (Chill Wills), who always gets the better of them, talks them into taking a nondescript horse in lieu of some of their wages. Ben finds that the horse is un-rideable, he comes up with the idea of taking it to a rodeo and betting other cowhands they cannot ride it.