Genesis 24:4 (KJV)

And 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:

And I will make thee swear by the Lord, 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:

But thou shalt go unto my country, and to my kindred, and take a wife unto my son Isaac.

And 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?

And Abraham said unto him, Beware thou that thou bring not my son thither again.