A Roman augur in the reign of Tarquin the Elder. When he forbade the king to increase the number of the tribes without consulting the augurs, Tarquin asked him if the thought then in his mind was feasible. “Undoubtedly,” said Accius. “Then cut through this whetstone with the razor in your hand.” The priest gave a bold cut, and the block fell in two. This story (from Livy, Bk. i., chap. 36) is humorously retold in Bon Gaultier's Ballads.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894