“Your slave is in your hands,” Abram said. “Do with her whatever you think best.” Then Sarai mistreated Hagar; so she fled from her.
Genesis 16:6 (NIV)
In a single verse, both the "sin of omission" and the "sin of commission" come into play. Sarai sins in her treatment of Hagar; Abram sins in his failure to stop her.
Both are guilty.