In the Bible "righteousness" describes right standing before God, and Genesis 15 records the earliest place where a person is said to be counted righteous — Abram, for believing God.
Genesis 15:6 in the King James Version reads:
And he believed in the LORD; and he counted it to him for righteousness.
The verse appears in Genesis 15, after God's promise to Abram of countless descendants. Read it in context at Genesis 15:6, or the full chapter at Genesis 15. Encyclopedia entry: en.wikipedia.org/wiki/Righteousness.