Who said "Beware of the man with a fixed purpose."?

This quote is attributed to Ishmael.

Beware of the man with a fixed purpose. - Ishmael

"Beware of the man with a fixed purpose."

Ishmael

Character in Moby-Dick

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"Call me Ishmael."

"Some certain significance lurks in all things, else all things are little worth."

"It is the whale's intrinsic nature to be wondrous."

"Better to sleep with a sober cannibal than a drunken Christian."