Judaism & Christianity started with God's Covenant with Abraham.
No, he predated Christianity. He was Jewish.
Judaism.
Judaism and Christianity.
Judaism, Christianity, and Islam religions.
Abraham
Because He is the father of Judaism
Abraham.
The common ancestor of the three religions Judaism, Christianity and Islam was Abraham
Christianity and Islam both have roots in Judaism. Abraham's son Issac was the ancestor of Jesus. Abraham's son Ishmael was the ancestor of Muhammad.
For Judaism: http://judaism.answers.com/jewish-history/a-biography-of-abraham
Christianity follows Abraham as a model example of faith. The book of Hebrews in the New Testament uses Abraham as a role model of obedience and faith to God. Abraham was commanded by God to leave his fathers land and enter into a new land by faith only.