These somewhat old-fashioned words contain the idea of "from" or "to." Whence means "from which place" or "from which position." Whither means "to what place, condition, or position." Few occasions arise for the use of either whence or whither, but when one or the other is needed, omit from or to: "Whence have you come?" "Whither are you going?" See also from whence.
Dictionary of problem words and expressions. Harry Shaw. 1975.