'Righteousness' in the Bible

If you have knowledge that he is upright, it is clear to you that everyone who does righteousness is his offspring.

My little children, let no man take you out of the true way: he who does righteousness is upright, even as he is upright;

In this way it is clear who are the children of God and who are the children of the Evil One; anyone who does not do righteousness or who has no love for his brother, is not a child of God.