From left to right: Abimelech, Abraham, Sarah (holding Isaac), and Hagar.  

Abimelech's friendly posture towards Sarah reflects his taking of Sarah while in Gerar.  

Abraham's friendly posture towards Abimelech reflects the oath they swore at Beersheba.  

Sarah's posture towards Hagar reflects her sending away of the maidservant and Ishmael into the wilderness of Beersheba.

The stories are told in Genesis 20-21.