Genesis 34:27

The sons of Jacob came upon the slain, and spoiled the city, because they had defiled their sister.

The verse describes the sons of Jacob, including Simeon and Levi together with their brothers, coming upon the slain and plundering the city of Shechem after killing its men in retaliation for the violation and defilement of their sister Dinah. They carried out that slaughter by deception and with a cruelty that brought a whole city to ruin. Jacob did not know of their plan until they had already carried it out.

The sons were not all righteous, and were affected to some degree by idolatry. Although provoked by the Shechemites' deed of disgrace, their revenge was cruel, grievously sinful and wrong. It was not sanctioned or approved by God.

Jacob rebuked them because their violence put him and his household in danger from the surrounding peoples. Their fierce anger and cruel wrath were condemned in Jacob's declaration that they would be divided and scattered among Israel. That scattering was fulfilled in that Simeon became Israel's smallest tribe with only a small portion within Judah's territory, while Levi received scattered cities rather than a tribal territory. Levi's later faithfulness to God in a time of apostasy brought the tribe sacred service in the sanctuary, turning its curse into a blessing.