Then He said to Abram: "Know certainly that your descendants will be strangers in a land that is not theirs, and will serve them, and they will afflict them four hundred years.
Genesis 15:13
Surrounding context
15:12 Now when the sun was going down, a deep sleep fell upon Abram; and behold, horror and great darkness fell upon him.
15:13 Then He said to Abram: "Know certainly that your descendants will be strangers in a land that is not theirs, and will serve them, and they will afflict them four hundred years.
15:14 And also the nation whom they serve I will judge; afterward they shall come out with great possessions.