Bridle Your Tongue!
I said, I will be careful about how I live, I will not sin by what I say. I will keep my mouth closed when I am near sinful people. Psalms 39:1 NIV
There are times when we need to be silent. We can say things that will affect an unbeliever. There will be times when God will tell you exactly what to say and when to say it. Then there will be times when he will instruct you to just listen. Be obedient to the spirit of the Lord.