1 Corinthians 14:22

Thus tongues are a sign not for believers but for unbelievers , while prophecy is a sign not for unbelievers but for believers .

Tongues, then, are a sign, not for believers but for unbelievers; prophecy, however, is not for unbelievers but for believers.

Wherefore tongues are for a sign, not to them that believe, but to them that believe not : but prophesying serveth not for them that believe not, but for them which believe.