Genesis 24:2 - 3
NKJV - 2 So Abraham said to the oldest servant of his house, who ruled over all that he had, "Please, put your hand under my thigh. 3 And I will make you swear by the LORD, the God of heaven and the God of the earth, that you will not take a wife for my son from the daughters of the Canaanites, among whom I dwell.
For follow-up discussion and general commentary on the topic. Comments are sorted chronologically.