Av Harachamim or Abh Haraḥamim (אב הרחמים "Father [of] mercy" or "Merciful Father") is a Jewish memorial prayer which was written in the late eleventh or early twelfth century, after the destruction of the Ashkenazi communities around the Rhine River by Christian crusaders during the First Crusade.
[1] First appearing in prayer books in 1290, it is printed in every Orthodox siddur in Nusach Sefarad and Nusach Ashkenaz, and it is recited in the Eastern Ashkenazic rite as part of the weekly Shabbat services except on special shabbatot, and in the Western Ashkenazic rite on the Shabbat before Shavuot and Tisha B'Av.
[2][3] The Yizkor service on Jewish holidays concludes with the Av Harachamim, which prays for the souls of all Jewish martyrs.
קְהִלּוֹת הַקּדֶשׁ שֶׁמָּסְרוּ נַפְשָׁם עַל קְדֻשַּׁת הַשֵּׁם הַנֶּאֱהָבִים וְהַנְּעִימִים בְּחַיֵּיהֶם וּבְמותָם לא נִפְרָדוּ.
וְנִקֵּיתִי דָּמָם לא נִקֵּיתִי וַיהוָה שׁכֵן בְּצִיּון: וּבְכִתְבֵי הַקּדֶשׁ נֶאֱמַר לָמָּה יאמְרוּ הַגּויִם אַיֵּה אֱלהֵיהֶם.