Pesukei dezimra
The first source for "pesukei dezimra" is in the Babylonian Talmud, where it is described as non-obligatory (performed by some people but not others):
Later commentaries explain what "pesukei dezimra" consists of: Rashi said it means psalms 148 and 150, Saadia Gaon said it means psalms 135, 148, 149, 150, while Meiri and Maimonides said it means all of psalms 145-150. Nowadays, it is customary for "pesukei dezimra" to include psalms 145-150 as well as several other psalms and recitations and blessings before ("Barukh she'amar") and after (Yishtabach) of "pesukei dezimra". Elsewhere, the Talmud states that a person should praise God and only afterwards begin his prayer. Opinions differ as to which praise is referred to: the first three blessings of the Amidah, the Shema blessings, or to "pesukei dezimra". For a long time, these prayers remained optional. Maimonides said that prayer should be recited in an upbeat mood, and as a result, these prayers became a part of the regular service. Maimonides also said that these prayers should be recited slowly and wholeheartedly, and that rushing through them as many who recite them daily do defeats their purpose. Rashi commented Talmud Berakhot 4b that "Three times" is prayer that is psalm 145 is personal Jewish prayer what is said three times a day. Rashi considered that singing of three psalms 145, 148, 150 in the morning is Jewish personal prayer (not communal). Maimonides considered the same, that communal prayer begins just starting from Kaddish and Shema. On Shabbat, holidays of biblical origin, and Hoshana Rabbah, various psalms are added between "Hodu" and "Yehi Khevod". The reason for additions is that no one has to rush off to work on these days, thereby allowing extra time for praise. Ashkenazi Judaism includes the following psalms in the following order: 19, 33, 34, 90, 91, 135, 136, 92, and 93. Sephardic Judaism includes the following psalms in the following order: 103, 19, 33, 90, 91, 98, 121, 122, 123, 124, 135, 136, 92, and 93.
On Shabbat and Yom Tov, "Nishmat" is inserted between the Song of the sea and the closing blessing. Following Nishmat, Shochein Ad is inserted. On Shabbat, the "chazzan" is changed prior to the recitation of Shochein Ad. On Yom Tov, this occurs one paragraph earlier ("Hakel B'Tzatzumot"). On High Holidays, the new chazzan takes over at the word "Hamelekh" ("the King"). There are questions in orthodox circles as to whether women are required or even permitted to recite pesukei dezimra, given that it is considered by some to be a timebound commandment. The opinions either require women to recite it completely, prohibit its recitation among women, allow but not require its recitation, or allow its recitation but prohibit Barukh She'amar and Yishtabach from being recited. Ashkenazi Judaism considers "pesukei dezimra" to be an obligation on the basis that it is not timebound, and it can be recited at any time of day. Opinions in Sephardic Judaism are divided. Some opinions allow women to recite "pesukei dezimra" without its accompanying blessings.
Origin
Pesukei dezimra, or zemirot as they are called in the Spanish and Portuguese tradition, are a group of praises that may be recited daily during Jewish morning services. They consist of various blessings, psalms, and sequences of verses. The purpose of "pesukei dezimra" is so an individual will recite praises of God prior to making requests of God in prayer which take place later during shacharit and throughout the day.