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In the Bible (specifically Genesis 16-21) and the Koran, the son of Abraham and his wife Sarah's maid Hagar. Sarah had told Abraham to conceive an heir with Hagar, but acording to the Bible, some time later when Sarah conceived a son with Abraham herself, Isaac, Sarah had Ishamel and his mother thrown out of Abraham's household. Abraham was not originally happy with this until God told him to do so. The two go off with minimal provisions, and are close to dying of thirst in the desert until an angel alerts Hagar to the existence of a well.

The version of the story in the Koran apparently has the journey of Hagar and Ishmael into the wilderness taking places when Ishmael was just a baby, before Isaac could have been born. (Though the Koran also has Abraham being told by God to sacrifice Ishmael, rather than Isaac as is stated in the Old Testament. The son to be sacrificed was rather older than babyhood in both versions of the story, so Abraham would have had to have been in contact with both his sons. This goes along with Muslim tradition, which traces the lineage of Arabic Muslims back to Abraham through Ishmael, and says that both Abraham's sons are part of the covenant God made with Abraham.)