Does a man's saying to another, "If you wait until she grows up, marry her" (meaning his daughter who is not yet born), after the other joked with him, "Will you marry your daughter to me?", constitute a valid marriage contract?

The conversation between the two men is idle talk and does not constitute a marriage contract because the intended bride is not yet in existence and is still a fetus. Al-Shafi'i said: "And if a man says to a woman, 'I have married you to the fetus of my wife,' and the woman accepts, or 'the first child my wife gives birth to,' and the woman accepts, or if a man says to another man concerning his wife's pregnancy, 'I have married you to the first girl my wife gives birth to,' and the man accepts, none of this ever constitutes a marriage contract, and there is no marriage for one who has not yet been born."