Matthew 12:37:

For by thy words thou shalt be justified, and by thy words thou shalt be condemned.

See also:

Say What
Objection: It Is Presumption to Think That Life and Death Are in Your Power
Objection: If Proverbs 18:21 Meant What Faith Preachers Say It Does, Old Testament People Could Have Gone Around Speaking Health to the Sick and Death to Cancer and Other Diseases Before Jesus Came
Objection: Occult Practitioners Attempt to Confess Things into Existence and Speak to Material Things to Make Them Change