A possible candidate for the story you have in mind is the legend of Lycaon:
In Greek mythology, Lycaon (/laɪˈkeɪɒn/; Greek: Λυκάων) was a king of Arcadia, son of Pelasgus and Meliboea, who, in the most popular version of the myth, tested Zeus by serving him the roasted flesh of his son Nyctimus, in order to see whether Zeus was truly omniscient. In return for these gruesome deeds, Zeus transformed Lycaon and his offspring into the forms of a wolf; Nyctimus was restored to life.
Lycaon (Arcadia). (2016, December 12). In Wikipedia, The Free Encyclopedia. Retrieved 21:11, December 12, 2016, from https://en.wikipedia.org/w/index.php?title=Lycaon_(Arcadia)&oldid=754471710
Callisto, Lycaon's daughter by some accounts, was also transformed to an animal - a bear this time. You may find more details about the myths, including lists of sources, on the excellent resource theoi.com:
The story of the Neuri people - as told by Herodotus - may also be of interest:
The Neuri follow Scythian customs; but one generation before the advent of Darius' army, they happened to be driven from their country by snakes; for their land produced great numbers of these, and still more came down on them out of the desolation on the north, until at last the Neuri were so afflicted that they left their own country and lived among the Budini. It may be that these people are wizards; for the Scythians, and the Greeks settled in Scythia, say that once a year every one of the Neuri becomes a wolf for a few days and changes back again to his former shape. Those who tell this tale do not convince me; but they tell it nonetheless, and swear to its truth.
Herodotus, The Histories (4.105), with an English translation by A. D. Godley. Cambridge. Harvard University Press. 1920