The Vilna Gaon and the Minor's Kiddushin
The Vilna Gaon tells the author of Teshuvos Shmuel that a minor's kiddushin is meaningless, and one hint about Maseches Parah settles the scholars' challenge.
The author of the Teshuvos Shmuel wrote a responsum discussing the halachah of a minor child performing an act of kiddushin. He held that if a minor boy gave a girl an object of value to effectuate kiddushin and marry her, we should be stringent and require a get. The Vilna Gaon read this teshuvah and remarked, “From your writings I can see that you are a brilliant scholar. However, the halachah is that we are not concerned with the actions of a minor attempting to perform kiddushin.” The Vilna Gaon was noting that one’s brilliance does not always lead him to decide the halachah in the right manner.
The Teshuvos Shmuel’s chaveirim found a clear passage in the Yerushalmi that seemed to support his opinion. A beraisa states that if a minor performed kiddushin in the presence of others, Rebbe Yishmael the son of Rebbe Yochanan ben Brokah says that the kiddushin is valid. The scholars wanted to ask the Vilna Gaon about this passage that directly supported the Teshuvos Shmuel’s opinion, so they asked the Vilna Gaon’s son Rebbe Avraham to ask him about it. Upon being questioned, the Vilna Gaon told his son that he was aware of that passage. Besides being in the Yerushalmi, it is also in the Tosefta of Mesechta Parah.