In Greek mythology, Hermes exchanged his lyre with Apollo for the cattle he stole.
The episode appears in the Homeric Hymn to Hermes. On the day of his birth, the infant Hermes left his cradle, found Apollo’s cattle, and devised a way to conceal the herd’s tracks. Apollo eventually discovered the theft and confronted him.
Hermes then revealed the lyre he had made from a tortoise shell and offered it to Apollo. Apollo was delighted by the instrument and accepted it in exchange for the cattle. The story explains why the lyre became especially associated with Apollo in Greek myth, even though Hermes is credited with inventing it.
This exchange is different from the later tradition that links Hermes with the caduceus. The lyre-and-cattle bargain is specifically the central resolution of the Homeric Hymn to Hermes.