Rashi on Genesis 22:13/רש"י על בראשית כ״ב:י״ג

1והנה איל BEHOLD, A RAM — It was predestined for that purpose from the six days of Creation (Avot 5:5; Midrash Tanchuma, Vayera 23).

2אחר AFTER the angel had said to him “Lay not thy hand upon the lad” he saw it being caught in the thicket. And that is what we mean when we translate it in the Targum by “And Abraham lifted up his eyes after these (i.e. after these words)”. Other versions of Rashi have: according to the Midrashic explanation, after means after all the words of the angel and the Shechinah, and after all the arguments of Abraham.

3בסבך IN A THICKET— a tree.

4בקרניו BY ITS HORNS — because it was running towards Abraham, but Satan caused it to be caught and entangled among the trees (Pirkei DeRabbi Eliezer 31).

5תחת בנו IN THE STEAD OF HIS SON — Since it is written, “He offered it up for a burnt offering”, surely nothing is missing in the text; what then is the force of “in the stead of his son”? At every sacrificial act he performed on it he prayed saying, “May it be Thy will that this act may be regarded as having been done to my son — as though my son is being slain; as though his blood is being sprinkled; as though his skin were being flayed; as though he is being burnt and is being reduced to ashes” (Genesis Rabbah 56:9).