1 Corinthians 14:21-22

14:21 It is written in the law: “By people with strange tongues and by the lips of strangers I will speak to this people, yet not even in this way will they listen to me,” ¹  says the Lord. 14:22 So then, tongues are a sign not for believers but for unbelievers. Prophecy, however, is not for unbelievers but for believers.

[14:21]  ¹ sn A quotation from Isa 28:11-12.