The Whiskey Sour cocktail is a variation of the Brandy Sour. Although "Sours" were introduced by Jerry Thomas in 1862 in "Bar-tenders guide: How to mix drinks", the whiskey variant did not appear until 1874 in "American Bar-Tender or The Art and Mystery of Mixing Drinks" by E.A. Simmons. A little later, Jerry Thomas introduced it in the 3rd edition of his famous "Bar-tenders guide" in which he specifies that the whiskey to be used is bourbon or rye.
Note that there is also the "Scotch sour" which is made with Scotch whiskey instead of bourbon or rye.