Did Abraham do wrong?

Modern scholars and pastors almost all teach that Abraham sinned against God and against his wife Sarah when he lacked faith and "played the coward". But nobody in the Bible - neither the Prophets nor Jesus nor the Apostles - see it that way. They all tell us that Abraham "learned faith" in his walk with God. According to them, Abraham was the supreme example of faith for all of us. We've been applying our arbitrary ethics and shifting standards to the Patriarch's life, and coming to the opposite conclusion from God's declaration about Abraham. The reason we have to honor the Patriarch is that God has pronounced a curse against anyone who dishonors his friend Abraham - the Prophet of God. "Those who are of faith are blessed along with Abraham, the man of faith." (Galatians 3:9)