1 Corinthians 14:11

11IfἐὰνthereforeοὖνnotμὴI knowεἰδῶtheτὴνpowerδύναμινof theτῆςsoundφωνῆς,I will beἔσομαιto the [one]τῷspeakingλαλοῦντιa foreignerβάρβαροςandκαὶthe [one]ὁspeakingλαλῶνtoἐνmeἐμοὶa foreignerβάρβαρος.

Therefore unless I know the power of the voice, I will be a barbarian to the one speaking, and the one speaking, a barbarian to me.