Genesis 24:5-9

The servant asked him, “What if the woman is unwilling to come back with me to this land? Shall I then take your son back to the country you came from?” “Make sure that you do not take my son back there,” Abraham said. “The LORD, the God of heaven, who brought me out of my father’s household and my native land and who spoke to me and promised me on oath, saying, ‘To your offspring I will give this land’—he will send his angel before you so that you can get a wife for my son from there. If the woman is unwilling to come back with you, then you will be released from this oath of mine. Only do not take my son back there.” So the servant put his hand under the thigh of his master Abraham and swore an oath to him concerning this matter.