Sure there was. Isaac himself got to witness the greatness of his father Abraham's faith. This incident was also penned down in Scripture by Moses. Therefore, multitudes of readers in later centuries could also see the greatness of Abraham's faith. He trusted in the Lord to the point where he would even give up his dearly beloved son. Such a man can justly be called the father of our faith.
Romans 3-5 is the place in Scripture where the doctrine of justification is defined in the most comprehensive manner. Indeed, it is the Apostle Paul who speaks of this subject more than any other biblical writer. There is no evidence here for the notion of justification being a lengthy, complicated process. According to Hebrews 11:8, Abraham was justified in Genesis 12: