Why were Ishmael and Hagar banished to the desert?

One day Sarah saw Ishmael taunting her some Isaac, and she became jealous and worried that Ishmael would claim Isaac's inheritance. And so she asked Abraham to banish Hagar and Ishmael. They were sent into the desert with just a little bread and water. Hagar and Ishmael survived thanks to the help of God. Tradition holds that they found refuge near Mecca, at the well of Zamzam.