The Odyssey by Homer Book 5 Page 11

Ulysses shuddered as he heard her. “Now goddess,” he answered, “there is something behind all this; you cannot be really meaning to help me home when you bid me do such a dreadful thing as put to sea on a raft. Not even a well found ship with a fair wind could venture on such a distant voyage: nothing that you can say or do shall make me go on board a raft unless you first solemnly swear that you mean me no mischief.”

Calypso smiled at this and caressed him with her hand: “You know a great deal,” said she, “but you are quite wrong here. May heaven above and earth below be my witnesses, with the waters of the river Styx — and this is the most solemn oath which a blessed god can take — that I mean you no sort of harm, and am only advising you to do exactly what I should