If Abraham knew that God forbidd murder (Genesis 9:5-6), why didn't he find it strange when God asked him to murder his son? (Genesis 22)?

Because, as He said, He knew God would provide a sacrifice,

Gen 22:6 So Abraham took the wood of the burnt offering and laid it on Isaac his son; and he took the fire in his hand, and a knife, and the two of them went together. 7 But Isaac spoke to Abraham his father and said, “My father!”

And he said, “Here I am, my son.”

Then he said, “Look, the fire and the wood, but where is the [b]lamb for a burnt offering?”

8 And Abraham said, “My son, God will provide for Himself the lamb for a burnt offering.” So the two of them went together.

Isaac was the son of promise, Abraham had faith that somehow God would make this right

And He did

11 But the Angel of the Lord called to him from heaven and said, “Abraham, Abraham!”

So he said, “Here I am.”

12 And He said, “Do not lay your hand on the lad, or do anything to him; for now I know that you fear God, since you have not withheld your son, your only son, from Me.”

13 Then Abraham lifted his eyes and looked, and there behind him was a ram caught in a thicket by its horns. So Abraham went and took the ram, and offered it up for a burnt offering instead of his son. 14 And Abraham called the name of the place, [c]The-Lord-Will-Provide; as it is said to this day, “In the Mount of the Lord it shall be provided.”

If Abraham actually existed, he was most likely suffering from delusions, visual/auditory hallucinations, etc.

Abraham saw beyond the obvious. He knew that YHWH could resurrect his son. Abraham also knew Genesis 3:15. He knew that YHWH had a good purpose in taking that test with him to solidify his friendship with YHWH. Abraham knew that the serpent (Satan the Devil) was the cause of the misfortune of Adam and Eve and their offspring. Abraham realized that for a murder there must be an Abraham saw beyond the obvious. He knew that YHWH could resurrect his son. Abraham also knew Genesis 3:15. He knew that YHWH had a good purpose in taking that test with him to solidify his friendship with YHWH. Abraham knew that the serpent (Satan the Devil) was the cause of the misfortune of Adam and Eve and their offspring. Abraham realized that for a murder there must bethere must be a brake there must be a brake  an EYE FOR EYE, FOOT FOR FOOT, TOOTH FOR TOOTH law "and that" Someone "should fulfill this PERFECT LAW of God.

What matters is that at the time "h", YHWH prevented him from this atrocious act and called him; THOU ART MY FRIEND. God (YHWH) is love. 1 John 4: 8, but this prophetic drama showed YHWH sacrificing his Son to fulfill the PERFECT LAW. Exodus 21: 24, 25, Deuteronomy 19: 21. Therefore, YHWH did not murder his son, it was a RESCUE . John 3:16  EYE FOR EYE, FOOT FOR FOOT, TOOTH FOR TOOTH law "and that" Someone "should fulfill this PERFECT LAW of God.

What matters is that at the time "h", YHWH prevented him from this atrocious act and called him; THOU ART MY FRIEND. God (YHWH) is love. 1 John 4: 8, but this prophetic drama showed YHWH sacrificing his Son to fulfill the PERFECT LAW. Exodus 21: 24, 25, Deuteronomy 19: 21. Therefore, YHWH did not murder his son, it was a RESCUE . John 3:16

IT WAS A TEST OF OBEDIENCE AND GOD DID not let him go through with it.

Ta Da!!!!!!!

They'll come up with some ridiculous argument.

The purpose of that fable is to teach blind unquestioning obedience.

Smeagol killed his brother for the ring, was that Sauron's or Satan's fault?