This Bible contradiction is from the Skeptic's Annotated Bible.
1 Corinthians 14:2-5 View context
For he that speaketh in an [unknown] tongue speaketh not unto men, but unto God: for no man understandeth [him]; howbeit in the spirit he speaketh mysteries.
But he that prophesieth speaketh unto men [to] edification, and exhortation, and comfort.
He that speaketh in an [unknown] tongue edifieth himself; but he that prophesieth edifieth the church.
I would that ye all spake with tongues, but rather that ye prophesied: for greater [is] he that prophesieth than he that speaketh with tongues, except he interpret, that the church may receive edifying.
1 Corinthians 14:39 View context
Wherefore, brethren, covet to prophesy, and forbid not to speak with tongues.
1 Corinthians 14:8-9 View context
For if the trumpet give an uncertain sound, who shall prepare himself to the battle?
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.