Six Black Horses

Audie and Dan Duryea are hired by a mysterious woman to take her across Indian country to her husband. On route, she tries to seduce Audie by offering to give him Duryea's share of the money if he will help her achieve her real goal: kill Duryea for having killed her husband. Audie dreams of a getting enough money to buy a ranch of his own, but his loyalty to his friend prevails... (imdb)