Two passages come to mind. The first is the parable of two sons in Matt 21:28ff and the Lord's question, "Which one did the will of his father?" It wasn't the words that mattered in that parable, but the deeds.

But words are not without effect! Because the very next passage that sprang to mind was Jesus' address to the gathered crowd after having rebuked the Pharisees for the same thing:

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It is not what enters into the mouth that defiles the man, but what proceeds out of the mouth, this defiles the man (Matthew 15:11 - see also the explanation in verses 17-20).

We are condemned by our words only if we fail to follow through with deeds in keeping with our words. Words matter! For we will be judged for every idle word we speak! So the old common wisdom that says, "words don't matter, only deeds," is NOT what is being suggested by the scripture.