I that am cruel am yet merciful;
I would not have thee linger in thy pain.
– William Shakespeare
Othello, Act 5, Scene 2. Othello believes that he is somehow doing the right thing and being just in killing Desdemona. He says these words after smothering her in her bed and then discovering that she is not quite dead. She will live a few minutes more to declare her innocence and express her devotion to the murdering Othello.