Deuteronomy 7:7

To wit, at that time when God first declared his love to you, and choice of you for his peculiar people, which was done to Abraham. For Abraham had but one son concerned in this choice and covenant, to wit, Isaac, and that was in his hundredth year; and Isaac was sixty years old ere he had a child, and then they had only two children; and though Jacob had twelve sons, yet it was a long time ere they made any considerable increase. Nor do we read of any great multiplication of them till after Joseph's death, Exodus 1:6,7.