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Kedushah is the name of several prayers recited during Jewish prayer services. They have in common the recitation of two Biblical verses - Isaiah 6:3 and Ezekiel 3:12. These verses come from prophetic visions in which angels sing the verses, "Holy, Holy, Holy" as praises to God.
There exist several variations of the Kedushah, which appear in different contexts and have different laws. The best-known Kedushah is recited in the Amidah. Another is recited in the Yotzer ohr blessing, and a third is recited on various occasions including the conclusion of weekday Shacharit. In some versions of the kedushah, additional Biblical verses are added in the same format as the verses from Isaiah and Ezekiel.