The longer version recited on Mondays and Thursdays is traced by classical sources (see e.g., S. Baer, Siddur Avodath Yisrael) to three sages who had escaped the destruction of the Jewish community in the Holy Land by the Romans. While on a ship on the way to Europe, they were caught in a storm, and all three recited a personal prayer, after which the storm subsided.
The longer version recited on Mondays and Thursdays is traced by classical sources (see e.g., S. Baer, Siddur Avodath Yisrael) to three sages who had escaped the destruction of the Jewish community in the Holy Land by the Romans. They were caught in a storm at sea while traveling to Europe and prayed together, after which the storm ceased.