1 Kings 15:26
And he did evil in the sight of the LORD, and walked in the way of his father, and in his sin wherewith he made Israel to sin. And he did evil in the sight of the LORD, and walked in the way of his father, and in his sin wherewith he made Israel to sin.
Nadab did evil in the sight of the Lord by following the sinful course of his father Jeroboam. He walked in the way Jeroboam had walked before him, holding to the same disobedient path. He continued the idolatrous worship that Jeroboam had introduced, the very sin by which Jeroboam had caused Israel to sin.