The tongue - tool for blessing or for evil!
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The closest you can come to this saying is in Revelation 1:16. In the Lord's case the two-edged sword is one of judgement - blessing on one "edge" and cursing on the other.
For people it often means our ability to bless God and curse our fellow man. This is hypocrisy. James uses some different metaphors to say the same thing:
James 3:8-12 But no man can tame the tongue. It is an unruly evil, full of deadly poison. With it we bless our God and Father, and with it we curse men, who have been made in the similitude of God. Out of the same mouth proceed blessing and cursing. My brethren, these things ought not to be so. Does a spring send forth fresh water and bitter from the same opening? Can a fig tree, my brethren, bear olives, or a grapevine bear figs? Thus no spring yields both salt water and fresh.
I hope you have found this helpful.