265 Responsum that was answered by the Congregation of Rome about the Song of the Sea, meaning, "And He saved"

Know that it has been our custom, the custom of the entire congregation of Rome and the custom of all the congregation around us [to say] the Song at the Sea. And it is the custom of all the congregations of Sefarad from the day of the exile of Jerusalem until now to say it the whole year, each and every day except for Tisha B'Av, on which we do not say it on account of mourning. Likewise do we not say it in the house of a mourner all seven days. And the custom of our ancestors is Torah; and our Rabbis said in a few places in the Talmud of the Land of Israel, "A custom annuls a law." And all the more so this thing, which the law does not contradict, and there is no mention of it in the whole Talmud, and our rabbis have been accustomed to saying it. Because the songs are an obligation, it is incumbent upon us to say it every day. For Rabbi Yossi said, "May my portion be among those that finish Hallel every day." And the conclusion is that we say it in the verses of song (psukei dezimrah). Hence our rabbis ordained to say this song, about the fall of our enemies, with [the verses of song]; and to give praise to the One who does wonders and to bless His name before and after them. Before them is 'Blessed is the One that spoke (Barukh sheamar); and after them is 'Let Him be praised (Yistabach). Hence it is only fitting to prevent [it from being said] on Tisha beAv, because it is a day of falling - may the Omnipresent, in His mercy, raise us and raise the fallen Sukkah of David. And there are some people who wanted to sing it even in the house of a mourner, and say that it is not fitting to prevent it; but they could not do it because of the custom. And that which it is said in prayer books, that we do not say song on Rosh Hashanah and Yom Kippur is only said about Hallel, meaning that we don't say Hallel on Rosh Hashanah and Yom Kippur, but we are obligated to say the Song at the Sea. And may the Holy One enlighten our eyes with the light of His Torah. To here is the responsum.