Or HaChaim on Genesis 50:20/אור החיים על בראשית נ׳:כ׳

1 ואתם חשבתם עלי רעה, והאלוקים חשבה לטובה, "what you had planned as harm for me, G'd planned it for good, etc." The whole matter is comparable to that of a person who plans to give his friend a poisoned drink in order to kill him, but who mistakenly pours him a cup of wine. Legally speaking, such a person is not guilty before a human tribunal. Similarly, the brothers were not guilty before Joseph though they were guilty before a Heavenly Tribunal. It is possible that the forgiveness of the victim even to a Jewish criminal would not free the criminal from the death penalty if the deed had been committed under circumstances warranting such a verdict.