Shimon Ben Kapah (שמעון בן כפה) was mentioned by רב יצחק באר who wrote in the Siddur Avodas Yisrael (סדר עבודת ישראל, הרב יצחק בן אריה יוסף דוב (בער), עמ' 206, הוצאת), in name of an old manuscript siddur from the year 1407:

“I heard from Yehuda Bar Yaakov that Shimon Ben Kipa authored Nishmas until the words מִי ידמה לך (Mi Yidmeh Lach)”

This identifies him as the Simon that the Encyclopaedia Judaica says was referred to as Simon Caiaphas by Rabbeinu Tam who likewise maintained that Simon was the author of the Nishmat prayer recited on Sabbaths and Festivals.^[1]

כמו כן בפירוש המקובלים לסידור "מלאה הארץ דעה", הרב נפתלי הירץ טריביש (סדור מלאה הארץ דעה, הרב נפתלי הירץ טריביש, פירוש בסוף תפילת ) כותב: "נשמת. מצאתי כי שמעון בן כפה יסדו. י"א שמעון בן שטח"

This is because Pavlut came from the school of Shimeon Ben Shetach with whom its story is sometimes confused.

Vetzaruch Iyun (צריך עיון), as elsewhere in Machzor Vitri 325 it states that Shimon Kipa authored the Piyutim of Seder Avoda said on Yom Kippur. Shimon also authored some Yom Kippur liturgy and others while in a cave according to the Machzor Vitri (p. 282 Mahadurah Makitzei Nirdamim) which also confirms his authorship of Nishmas.

Compare with

שמעון כיפא שמעון בן כפה שמעון הקלפוס

שמעון כיפה

↑ Machzor Vitry, edited by S.Hurwitz, 1923[2], p.285 note 5 and p. 362 note 5. CF Urbach, Tosafot, 191–3. (Israel Moses Ta-Shma). CF. J. Eisenstein's articles on Simon Caiaphas in Otzar Israel and Otzar Midrashim {"page 34 of the Wipf and Stock Publisher's edition of New York Orthodox Rabbi Harvey Falk's book "Jesus the Pharisee: A new look at the Jewishness of Jesus" (copyright 1985 Paulist Press)} a Midrash brought in Otzer HaMidrashim p. 557 [1920, by Rav Y.D. Eizanshtein] Beis Hamidrash vol. 5/60 and vol. 6 [1860; Likkut of old Midrashim]

[1] Machzor Vitry, edited by S.Hurwitz, 1923[2], p.285 note 5 and p. 362 note 5. CF Urbach, Tosafot, 191–3. (Israel Moses Ta-Shma). CF. J. Eisenstein's articles on Simon Caiaphas in Otzar Israel and Otzar Midrashim {"page 34 of the Wipf and Stock Publisher's edition of New York Orthodox Rabbi Harvey Falk's book "Jesus the Pharisee: A new look at the Jewishness of Jesus" (copyright 1985 Paulist Press)} a Midrash brought in Otzer HaMidrashim p. 557 [1920, by Rav Y.D. Eizanshtein] Beis Hamidrash vol. 5/60 and vol. 6 [1860; Likkut of old Midrashim]

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