Explain how you know iniquity was in someone
Do you have a specific verse in mind?
Ultimately, somebody else's sin is sort of "none of our business" ... God is perfectly capable of dealing with sinners without our help. We have a ministry to help restore a fellow Christian that has stumbled into sin (Galatians 6:1-2), but that comes with a WARNING not to let THEIR sin drag us into sins of our own [
judgemental much? self-righteous much? harsh and unloving much?).
The classic Bible verse for worrying about SOMEBODY ELSE'S sin is:
Romans 14:1-13
Receive one who is weak in the faith, but not to disputes over doubtful things. For one believes he may eat all things, but he who is weak eats only vegetables. Let not him who eats despise him who does not eat, and let not him who does not eat judge him who eats; for God has received him. Who are you to judge another’s servant? To his own master he stands or falls. Indeed, he will be made to stand, for God is able to make him stand.
One person esteems one day above another; another esteems every day alike. Let each be fully convinced in his own mind. He who observes the day, observes it to the Lord; and he who does not observe the day, to the Lord he does not observe it. He who eats, eats to the Lord, for he gives God thanks; and he who does not eat, to the Lord he does not eat, and gives God thanks. For none of us lives to himself, and no one dies to himself. For if we live, we live to the Lord; and if we die, we die to the Lord. Therefore, whether we live or die, we are the Lord’s. For to this end Christ died and rose and lived again, that He might be Lord of both the dead and the living. But why do you judge your brother? Or why do you show contempt for your brother? For we shall all stand before the judgment seat of Christ. For it is written:
“As I live, says the LORD,
Every knee shall bow to Me,
And every tongue shall confess to God.”
So then each of us shall give account of himself to God. Therefore let us not judge one another anymore, but rather resolve this, not to put a stumbling block or a cause to fall in our brother’s way.