She, dying, gave it me;
And bid me, when my fate would have me wive,
To give it her. I did so: and take heed on ‘t;
Make it a darling like your precious eye.
– William Shakespeare
Othello, Act 3, Scene 4. Othello tells the backstory of the precious handkerchief given to his mother by an Egyptian charmer. When his mother was dying she passed it on to him to give it to his wife whenever he married. Using a simile, Othello ominously tells Desdemona to keep it close to her like her precious eye.