1 Corinthians 14:13 in the World English Bible
Therefore let him who speaks in another language pray that he may interpret.
Context
12 Even so ye, forasmuch as ye are zealous of spiritual gifts, seek that ye may excel to the edifying of the church.
13 Wherefore let him that speaketh in an unknown tongue pray that he may interpret.
14 For if I pray in an unknown tongue, my spirit prayeth, but my understanding is unfruitful.