On the Origin of And He, being merciful

The supplicatory prayer [known as] Ve-hu raḥum was composed by men of renown who were exiled from Jerusalem at [the time of] the destruction of the Second Temple, when Vespasian—may his bones rot—exiled them and ordered that they be split up [and placed on] three [separate] boats, and he secured them fast inside them without ship captains and set them adrift on the sea. Now, a wind buffeted them and cast them ashore onto dry land in every single region. One ship came ashore at Lepanto, one in the province of Arles, and one in the province of Bordeaux. Now, with regard to those who settled in Bordeaux, the ruler extended a warm welcome to them, giving them fields and vineyards; they remained there for a lengthy period of time until that ruler died. Then a new king rose to power over them, and whatever enactments the original [ruler] had made for their benefit, the new one abolished, and he declared fresh decrees against them. Now, there were two brothers there, Joseph and Benjamin, and with them was their cousin Samuel; they were citizens of Jerusalem, and they cried out to the Almighty when they were in dire straits, and constantly fasted and afflicted themselves, wearing sackcloth on their flesh; among the three of them, they composed [the prayer] Ve-hu raḥum.

Joseph composed from “And He, being merciful” up to “You are a gracious and merciful King,” and Benjamin composed from “We beseech You” up to “There is none like You,” and Samuel composed the remainder up to “The Lord is One.”

And subsequently the Almighty saved and redeemed them, and slew the enemy by means of an abnormal and painful death; and they sent dispatches and publicized the episode in its entirety wherever Jews resided, and additionally wrote out the prayer and informed them of it, and the [Jews] accepted upon themselves [the obligation] of reciting it on Mondays and Thursdays; and all of Israel has since adopted this practice.