The White Buffalo (1977)

Tormented by incessant and recurring nightmares of a hellish great white buffalo attacking him in the snow-clad wilderness, the ailing Wild Bill Hickok, decides to travel north to hunt down the raging mythical beast. Along the way, the experienced hunter will team up with an old friend, the one-eyed Charlie, while in the meantime, the Indian Chief Crazy Horse whose child was killed by the same creature, is already out in the unforgiving landscape, pursuing the extraordinary bison. Without a doubt, both men won't rest until they find the supernatural monster of legend, however, in this uncomfortable alliance, even the slightest mistake can prove deadly.

IMDb: https://www.imdb.com/title/tt0076915