Hermes Makes the First Lyre
After completing his new ritual -- sacrificial offering to the gods, the infant Hermes went back home. On his way, he found a tortoise, which he took inside his house. Using leather strips from Apollo's herd animals for the strings, Hermes created the first lyre with the shell of the poor reptile. He was playing the new musical instrument when big (half-)brother Apollo found him.
Hermes Trades With Apollo
Recognizing the material of the lyre's strings, Apollo fumed, protesting Hermes' cattle theft. He was smart enough not to believe his baby brother when he protested his innocence.
"Now when the Son of Zeus and Maia saw Apollo in a rage about his cattle, he snuggled down in his fragrant swaddling-clothes; and as wood-ash covers over the deep embers of tree-stumps, so Hermes cuddled himself up when he saw the Far-Shooter. He squeezed head and hands and feet together in a small space, like a new born child seeking sweet sleep, though in truth he was wide awake, and he kept his lyre under his armpit."
Homeric Hymn to Hermes IV.235f
Reconciliation seemed impossible until the father of both gods, Zeus, stepped in. To make amends, Hermes gave his half-brother the lyre. At a later date, Hermes and Apollo made another exchange. Apollo gave his half-brother
in exchange for a flute Hermes invented.