Baasha son of Ahijah, of the house of Issachar, conspired against him; and Baasha struck him down at Gibbethon, which belonged to the Philistines; for Nadab and all Israel were laying siege to Gibbethon.
So Baasha killed Nadab in the third year of King Asa of Judah, and succeeded him.
References for 1 Kings 15:28
As soon as he was king, he killed all the house of Jeroboam; he left to the house of Jeroboam not one that breathed, until he had destroyed it, according to the word of the Lord that he spoke by his servant Ahijah the Shilonite—
because of the sins of Jeroboam that he committed and that he caused Israel to commit, and because of the anger to which he provoked the Lord, the God of Israel.
Now the rest of the acts of Nadab, and all that he did, are they not written in the Book of the Annals of the Kings of Israel?