The Sages formulated the Al Ha-nisim prayer so that we may thank God for the salvation He performed for the Jewish people at the time of Purim. We recite it in the berakha of thanksgiving in the Amida and in the berakha of Nodeh Lekha (“We thank You”) in Birkat Ha-mazon. We do not mention Purim in the berakha of Me-ein Shalosh (“Al Ha-miĥya”).
If one forgets to recite Al Ha-nisim in the Amida or in Birkat Ha-mazon, he nonetheless fulfills his obligation. If, however, he remembers before concluding the berakha in which Al Ha-nisim is inserted, he should go back and recite it, unless he already said God’s name at the end of the berakha. In such a situation, it is proper to recite Al Ha-nisim at the end of the Amida, after the berakhot are completed, because one may add unlimited prayers of supplication and thanksgiving at that point. Similarly, one who forgets to recite Al Ha-nisim in Birkat Ha-mazon should recite it toward the end of the prayer, together with the Ha-Raĥaman passages, where one may add as many prayers of thanksgiving as he likes (Rema 682:1, mb ad loc. 4).
One who begins his meal on Purim but continues eating long into the night must recite Al Ha-nisim in Birkat Ha-mazon, because the beginning of the meal determines when the meal took place (sa 695:3; see mb ad loc. 16).
The Sages enacted that three people are called to the Torah on Purim to read the section beginning with “Amalek came” (Shemot 17:8-16). Even though one of Ezra’s enactments was that no less than ten verses may be read in a public Torah reading, we read nine on Purim because the entire account of Amalek’s attack on Israel contains only nine verses. Some have a custom to read the last verse twice in order to arrive at a total of ten verses (sa 693:4), while others do not (Rema ad loc.).
This halakha is highly suggestive. As long as Amalek’s name has yet to be blotted out, God’s name is not yet fully revealed. Therefore, when we read the section of “Amalek came,” we read only nine verses.
Even though the Jews experienced a great salvation on Purim, the Sages did not institute the recitation of Hallel on that day. The Talmud (Megilla 14a) provides three reasons for this. R. Yitzĥak explains that we do not recite Hallel for a miracle that occurred outside the Land of Israel. According to Rava, it is omitted because we remained subjugated to Aĥashverosh even after the miracle occurred, and Hallel can be said only over a salvation that brings us freedom. R. Naĥman maintains that the Megilla reading is considered like Hallel; therefore, there was no need to enact the recitation of Hallel.
One may not deliver eulogies or fast on the fourteenth and fifteenth of Adar, whether one lives in a walled or unwalled city. The only time one may deliver a eulogy is at the funeral of a Torah scholar, provided that the body is present (sa oĥ 696:3, yd 401:5).
We omit Taĥanun and La-menatze’aĥ from our prayers on both days of Purim (sa 693:3). We also omit Taĥanun from Minĥa on Ta’anit Esther, if it immediately precedes Purim (mb 131:33).
It is customary to wear Shabbat/Yom Tov clothing on Purim, both at night and during the day (Rema 695:2, Kaf Ha-ĥayim 695:13).
. Me’iri and Manhig state that, according to the opinion that the Megilla reading is in place of Hallel, one who cannot obtain a Megilla from which to read on Purim must recite Hallel instead. mt, Laws of Megilla and Ĥanuka 3:6, also seems to maintain that this reason is the primary one. However, some authorities write that the other answers are primary. Therefore, one who does not have a Megilla should, le-khatĥila, recite Hallel without a berakha, in order to satisfy all the opinions.