Genesis 15:16

And thou shalt go to thy fathers in peace; thou shalt be buried in a good old age. Abram himself would not be obliged to share in the afflictions which would come upon his children, but would die in peace, at an advanced age.

But in the fourth generation they shall come hither again; for the iniquity of the Amorites is not yet full. The generations at that time were still reckoned at approximately one hundred years, and so four generations would represent, in round numbers, four hundred years. By that time the iniquity of the Amorites, here named as the representatives of all the Canaanites, would be fulfilled, and their annihilation by the children of Israel would come upon them as the judgment of the Lord.