1 Kings 21:3
Naboth said to Ahab, "May Yahweh forbid me, that I should give the inheritance of my fathers to you!"
WEB
And Naboth said to Ahab, The LORD forbid it me, that I should give the inheritance of my fathers unto thee.
KJV
What 1 Kings 21:3 means
Naboth refuses to sell his vineyard because the land is not his to sell. It is the portion God assigned to his family, so handing it to the king would be a betrayal of God, and he answers with an oath.
Ahab, king of Israel, wants the vineyard next to his palace in Jezreel for a vegetable garden. He offers Naboth a better vineyard or a fair price. Naboth refuses, and the king goes home sullen, lies down facing the wall, and will not eat. Jezebel handles it. She writes letters in Ahab's name, stages a fast, seats false witnesses who accuse Naboth of cursing God and the king, and has him stoned. Ahab goes down to claim the land, and Elijah is standing in it.
Israel's land law explains the refusal. Land was allotted by tribe and clan and was meant to stay in the family permanently. Leviticus 25:23 has God saying the land is his and Israel are tenants on it; the Jubilee returned fields to their families, and Numbers 36 guards tribal boundaries. The word Naboth uses, nachalah, means the allotted portion, the same term used for Israel's share in God's gift. He cannot sell it even if he wanted to. Ahab is bound by that same law, which is why Jezebel, a Phoenician princess raised where kings simply take, has to manufacture a capital crime to get around it.
The refusal is an oath. The Hebrew phrase behind "May Yahweh forbid me" comes from a root about profaning what is holy, and it pulls God's name into the sentence. The sale would be a desecration, so the answer is closed before any price is named. "The inheritance of my fathers" finishes the thought: the vineyard belongs to the dead and the unborn as much as it belongs to Naboth.