The LORD’s word came to Jonah the second time, saying, “Arise, go to Nineveh, that great city, and preach to it the message that I give you.” So Jonah arose, and went to Nineveh, according to the LORD’s word. Now Nineveh was an exceedingly great city, three days’ journey across. Jonah began to enter into the city a day’s journey, and he cried out, and said, “In forty days, Nineveh will be overthrown!”
Traditional attribution
The book names Jonah as its subject, not its author. Attribution to Jonah is traditional.