OTHELLO: Give me a living reason she’s disloyal.
IAGO: I lay with Cassio lately;
And, being troubled with a raging tooth,
I could not sleep. There are a kind of men
So loose of soul that in their sleeps will mutter
Their affairs. One of this kind is Cassio.
In sleep I heard him say "Sweet Desdemona,
Let us be wary, let us hide our loves."
– William Shakespeare
Othello, Act 3, Scene 3. Iago invents a lie to inflame Othello’s jealousy over Desdemona, when Othello asks for proof of her disloyalty. Iago falsely claims that as he and Cassio shared a bed one night, Cassio called out in his sleep, addressed his "sweet Desdemona" and pleaded with her to keep their love affair a secret.