Dayyeinu (Hebrew, "It Would Have Been Enough") is the refrain of a song of thanksgiving in the Passover Haggadah .
The Dayyeinu song, in all rites, starts with the words: "How many are the favors that God has conferred upon us" and proceeds to enumerate 15 (in some rites 16) stages of the redemption of the Jews from Egyptian bondage, including their miraculous survival in the Sinai wilderness, their receiving the laws of Sabbath and the entire Torah, and finally, their being led into Ereẓ Israel and building the Temple. The origin of this litany is uncertain, although some scholars date it back to the late Second Temple period. No mention of it is made in the Talmud or inthe Midrash, although some scholars see an indirect reference to it in Shabbat 32b. It first appears in the siddur of Saadiah Gaon (ninth century C.E.). While some scholars believe that Dayyeinu was inspired by Sifrei Deuteronomy (337, 339, etc.), others hold the dependence to be in the opposite direction. The term "dayyeinu" is used ironically in Hebrew and in Yiddish and means "That's enough," "I've had enough."
Sources: Encyclopaedia Judaica. © 2008 The Gale Group. All Rights Reserved.
D. Goldschmidt, Ha-Haggadah shel Pesaḥ ve-Toledoteha (1960), 48–51; M. Kasher, Haggadah Shelemah (1967), 55–58; idem, Israel Passover Haggadah (1962), 134–41.