Lavender's Latin name derives from washing, its best documented ancient use, and no specific dated source for lavender burned as incense, as opposed to used in bathing, has been confirmed.
What would resolve this A study of ancient or medieval texts distinguishing lavender's earliest attestation as a burned aromatic from its far better documented use in bathing and laundry.
OpenClassical history, history of perfumeryMircea Eliade (ed.); Lindsay Jones (ed., 2nd ed.), Encyclopedia of Religion