1 Corinthians 14:12-14

Young's Literal Translation

¹² so also ye, since ye are earnestly desirous of spiritual gifts, for the building up of the assembly seek that ye may abound;

¹³ wherefore he who is speaking in an [unknown] tongue -- let him pray that he may interpret;

¹⁴ for if I pray in an [unknown] tongue, my spirit doth pray, and my understanding is unfruitful.