A promise to marry the friend's daughter in jest before he had any children

Question:
He says: Honorable Shaykh, may Allah grant you success. He says: I was joking with a friend of mine while we were eating, and he said to me, "If I had a sister, I would marry her to you." So I said to him, "I will marry your daughter, if Allah wills." He said, "It is done." Knowing that he has not married yet, nor have I, what is the ruling in this matter for the future?

Answer:
Praise be to Allah that he has no daughters. As long as he has no daughters, nothing has happened. If he has daughters later, you may ask then. But for now, as long as he has no daughters, leave it. Yes.