Hesiod's detailed account of Pandora opening her container appears in Works and Days.
Works and Days is an ancient Greek didactic poem traditionally attributed to Hesiod, who is generally dated to the late eighth or early seventh century BCE. It combines advice about farming and justice with myths explaining why human life includes labor and suffering.
The Pandora episode appears in the poem's discussion of the consequences of Prometheus's theft of fire. Zeus sends Pandora to Epimetheus, who accepts her despite Prometheus's warning. She then opens the container, releasing destructive conditions into the human world.
Hesiod also mentions Pandora in Theogony, but the fuller narrative about the container is associated with Works and Days. The work is not an epic poem like Homer's Iliad or Odyssey; it is a didactic poem with practical and moral instruction.