John Gill Commentary 1 Kings 21:3

"And Naboth said to Ahab, Jehovah forbid it me, that I should give the inheritance of my fathers unto thee." — 1 Kings 21:3 (ASV)

And Naboth said to Ahab, the Lord forbid it me that I should
give the inheritance of my fathers to you .
] The inheritances of families were not to be alienated to another family, or tribe, nor even to be sold, unless in extreme poverty, and then to return at the year of jubilee, (Leviticus 25:23Leviticus 25:28) . Now Naboth was a man in good circumstances, and under no necessity of selling his vineyard; and, if he sold it, he might reasonably conclude, it becoming a part of the royal demesnes, would never revert to his family; and therefore, both out of regard to the law of God, and the good of his family, would not part with it at any rate:

This shows that he was a conscientious man, and therefore is thought to be one of those that would not bow his knee to Baal, and against whom Ahab had a grudge, and sought an opportunity against him.