Abraham said to his servant, the oldest of his household who was in charge of all that he owned, “Please place your hand under my thigh, and I will make you swear by the Lord, the God of heaven and the God of earth, that you shall not take a wife for my son from the daughters of the Canaanites, among whom I live.
Genesis 24:2-3 (NASB)
Some rabbis wondered if “under my thigh” meant for the servant to grab hold of Abraham’s circumcision, as that was tied to covenant.
But many disagree, and suggest that “sitting on the hands” was symbolic of binding the servant to an action.