Genesis 24:2-9

2And Abraham said unto his eldest servant of his house, that ruled over all that he had, Put, I pray thee, thy hand under my thigh: 3And I will make thee swear by Yhwh, the God of heaven, and the God of the earth, that thou shalt not take a wife unto my son of the daughters of the Canaanites, among whom I dwell: 4But thou shalt go unto my country, and to my kindred, and take a wife unto my son Isaac. 5And the servant said unto him, Peradventure the woman will not be willing to follow me unto this land: must I needs bring thy son again unto the land from whence thou camest? 6And Abraham said unto him, Beware thou that thou bring not my son thither again.

7Yhwh God of heaven, which took me from my father’s house, and from the land of my kindred, and which spake unto me, and that sware unto me, saying, Unto thy seed will I give this land; he shall send his angel before thee, and thou shalt take a wife unto my son from thence. 8And if the woman will not be willing to follow thee, then thou shalt be clear from this my oath: only bring not my son thither again. 9And the servant put his hand under the thigh of Abraham his master, and sware to him concerning that matter.