Genesis 22:11-12. And the angel of the Lord called unto him (to
Abraham) out of the heavens, and said: "Abraham, Abraham." And he
(Abraham) said: "Here am I." And he (the angel) said: "Lay not your
hand upon the lad, nor do any thing to him; for now I know that you
are a God-fearing man, seeing as you have not withheld your son,
your only son, from Me."
And again later (vereses 15-18):
And the angel of the Lord called unto Abraham a second time from
the heavens, and said: "By Myself have I sworn, says the Lord, that
because you have done this thing, and have not withheld your son,
your only son, I will surely bless you, and I will surely multiply
your seed as the stars of the heaven, and as the sand which is upon
the seashore; and your seed shall possess the gate of his enemies;
and through your seed shall all the nations of the earth be
blessed; because you have hearkened to My voice."