Halakhah su Salmi 111:4

Whoever has had a miracle occur for them, and all the more so the inhabitants of a city, can establish, by popular agreement, for themselves and those who come after them to make that day into a “Purim”. And it seems to me that the meal which they make to commemorate the miracle is considered at the level of a seudat mitzvah [meal with halachic weight] ... So, too, do we practice regarding the miracle which was performed for us in the year 5564, the night of the 16th of Kislev. There was death in the courtyard in which I live because of a conflagration which started from gunpowder. Several houses in the courtyard fell, including one house that was mine. In the room where my whole family was located, two half-walls and one beam fell ... Not a single one (i.e. member of the family) did not shed at least some drops of blood. G-d in His mercy and kindness considered for us the blood like a sacrifice to atone, and saved us, and all of us remained alive. Even though I suffered a great loss of several hundred adumim (a currency), G-d in His kindness substituted blood for money [lit. damim for damim]. Aside from us, there were killed, in our many sins, in my courtyard, 31 people ... And in order to tell of the wonders of G-d, as it is written (Tehillim 111:4) “He created a memorial for His wonders”, I have accepted upon myself and my descendants, without vowing, on the 16th of Kislev, since in our land it is already a day of fasting in many communities for the chevra Kadisha who do kindness, to devote at least half of it for G-d, and whoever can should fast. And on the following night, immediately after Maariv they should gather and light candles like on Yom Tov and sing the Shir HaYichud slowly and pleasantly, and the Shir HaKavod with song, and afterwards [recite] chapters of Psalms slowly ... And after this to make a meal for those who learn Torah and to give charity in accordance with the blessing of G-d, as much as one can afford.