upon a windy tree
for nine whole nights,
wounded with a spear
and given to Othinn,
myself to myself for me;
on that tree
I knew nothing
of what kind of roots it came from.
They cheered me with a loaf
and not with any horn,
I investigated down below,
I took up the runes,
screaming I took them,
and I fell back from there.
Hávamál
(Thank you Duncan Alexander for the link and reference)