Hesiod's Works and Days contains the account of Pandora opening the vessel of evils.
Works and Days is a didactic poem that combines advice about farming and justice with myths explaining the human condition. Its Pandora episode appears in the poem's discussion of why suffering and difficult labor exist in the world. The vessel is opened after Pandora is sent to Epimetheus as part of Zeus's punishment.
Theogony, another work attributed to Hesiod, also mentions Pandora's creation but gives less of the familiar vessel narrative. This is why identifying the specific poem matters when tracing the complete story.
The poem is traditionally dated to the early archaic period of Greece. It is not a prose myth collection, and it does not use the modern phrase “Pandora's box.” Later translations and retellings condensed its details into the short story now familiar to international audiences.