The Norse poem that describes Odin’s self-sacrifice on Yggdrasil is Hávamál.
The episode appears in the poem’s Rúnatal, or “Odin’s Rune Song,” especially stanzas 138–146. Odin says that he hung on a “windy tree” for nine nights, wounded by a spear, without food or drink. He sacrificed himself to himself to gain the runes and the wisdom associated with them.
Hávamál means “Sayings of the High One” and is preserved in the 13th-century Poetic Edda, a manuscript collection of older Norse material. The poem combines advice, proverbial wisdom, accounts of magic, and mythic passages attributed to Odin.
The text does not actually name the tree as Yggdrasil, although commentators and scholars commonly identify it with the world tree. This detail can cause confusion: Yggdrasil is the cosmic tree, while Hávamál is the poem containing Odin’s sacrifice. The episode is also sometimes compared with crucifixion imagery, but that comparison concerns interpretation rather than the poem’s title.