15 He said, 'I swear by Myself, declares the Lord, because you have done this and have not withheld your son, your beloved son, from Me, I will surely bless you and make your descendants as numerous as the stars in the sky and as the sand on the seashore. Your descendants will take possession of the cities of their enemies, 16 and through your offspring, all nations on earth will be blessed, because you have obeyed me. And I have shown to all that you are faithful to me in everything I have said to you: Go in peace.' 17 Abraham returned to his servants, and they set off together for Beersheba, where Abraham lived by the Well of the Oath.
Pseudo Philo Biblical Antiquities 32:4
4 And when his father had placed him upon the altar and had bound his feet to kill him, the Almighty quickly sent forth his voice from above saying: "Do not kill your son, nor destroy the offspring of your body: for now I have made myself known to those who are unaware of me, and have silenced those who constantly speak ill of you. And your memory shall be before me forever, and your name and the name of this your son from one generation to another."
Notes and References
"... in interpreting in this way, these writers seemed to contradict what the Bible itself says explicitly later on. For in the biblical account, after Abraham has demonstrated his willingness to offer up his beloved Isaac, God says to him: 'Now I know that you fear God, since you have not withheld your son, your only son, from me' (Genesis 22:12). 'Now I know' seems to imply 'I did not know before.' How then could the author of Jubilees and other interpreters maintain that God did know all along? The answer lies in yet another ambiguity in the Hebrew. For the same consonants that spell the Hebrew word 'I know' can also be read in such a way as to mean 'I have made known' or 'I have notified.' This is apparently how some interpreters chose to understand the text ... Thus, God's great test of Abraham took place in response to a challenge and was carried out in order to prove Abraham's virtues not to God, but to others—Satan, the other angels, or the world at large ..."
Kugel, James L. The Bible as it Was (pp. 172-173) Harvard University Press, 1998