1 Corinthians 14:6-11 King James Version (KJV)
6 Now, brethren, if I come unto you speaking with tongues, what shall I profit you, except I shall speak to you either by revelation, or by knowledge, or by prophesying, or by doctrine?
7 And even things without life giving sound, whether pipe or harp, except they give a distinction in the sounds, how shall it be known what is piped or harped?
8 For if the trumpet give an uncertain sound, who shall prepare himself to the battle?
9 So likewise ye, except ye utter by the tongue words easy to be understood, how shall it be known what is spoken? for ye shall speak into the air.
10 There are, it may be, so many kinds of voices in the world, and none of them is without signification.
11 Therefore if I know not the meaning of the voice, I shall be unto him that speaketh a barbarian, and he that speaketh shall be a barbarian unto me.
1 Corinthians 14:27-28 King James Version (KJV)
27 If any man speak in an unknown tongue, let it be by two, or at the most by three, and that by course; and let one interpret.
28 But if there be no interpreter, let him keep silence in the church; and let him speak to himself, and to God.