It says in Mekor Baruch (of Rabbi Baruch Epstein)
The Rosh Yeshiva of Volozhin, the Netziv, was once sitting down surrounded by several high-caliber students – avrechim versed in Torah, wise, and filled with knowledge – who taught and knew how to reason deeply. The Rosh Yeshiva and his students were at that time dealing with a difficult problem, one that, as it turned out, the young Baruch Epstein provided an answer to.
The problem was as follows:
Two brothers shared a business for many years, and their relationship with one another was friendly and loving. However a dispute once arose between them, and the friction that it created led one of them to swear that he would never see his brother again. After several years, the second brother died, and the surviving one regretted the oath that he had taken. He wanted to return and see his dead brother and beg his forgiveness. He then came to see the Rav and asked whether his oath was valid now that his brother was dead. The Rav and his students began to discuss the matter, and some ruled that it was still valid while others ruled that it was not, yet they could not reach a definitive conclusion. It was then that the young Baruch, who was sitting among them, turned to his uncle the Rav and said, “There is a very simple solution to this, and it is explicitly written in the Torah. It states in Exodus, ‘Moses said to the people, “Do not fear…for the Egyptians you see today, you shall never see them again” ’ [Exodus 14:15]. Yet afterwards it is written, ‘Israel saw the Egyptians dead on the seashore’ [v.30]. From this we have a clear proof that viewing a person after his death is not called seeing, and therefore the brother’s oath does not apply to his dead brother.” Upon hearing this, the Rav arose, placed his hand on his nephew’s head, and said: “Happy is your youth.” This experience encouraged him to write Torah Temimah (from Rabbi Baruch’s memoirs: Mekor Baruch, Ch. 48, Par. 3)
Yet, the exact same story is told in the name of the Noda BeYehuda (In Noda BiYehuda by CIS publishers).
What's the source of the Noda BeYehuda making the above Chiddush?