Genesis 25:8

Then Abraham gave up the ghost, and died in a good old age, an old man, and full of years; and was gathered to his people.

Died in a good old age - in filfillment of the prediction (Genesis 15:15).

And was gathered to his people. This phrase (cf. Genesis 15:15; Judges 2:10) cannot mean simply burial, because the corpse of Sarah was the solitary tenant of the tomb; and it is applied here and elsewhere to an event which had taken place previous to the body being deposited in the family sepulchre (Genesis 35:29; Genesis 49:29-33; Numbers 20:24-29; Deuteronomy 32:50). It must imply a reunion in the place of souls apart from the lifeless body; and the fact of such a phrase being in popular use among the Hebrews, is decisive against the theory of Warburton, showing that the patriarchs did possess the knowledge of a future state (Genesis 47:9; cf. Hebrews 11:9-10; Hebrews 11:13-16; Matthew 12:31-32).