Saying Tehillim prior to Kol Nidrei:
Before the Chazzan begins Kol Nidrei, one recites nine chapters of Tehillim [chapter 115-123], following the tradition of the Baal Shem Tov, in name of his master and teacher, Achiya Hashiloni.
 Sefer Haminhagim [English] p. 113; Hayom Yom 1st of Elul
This custom was told to Tzemach Tzedek by his grandfather the Alter Rebbe when he was nine years old. The Alter Rebbe told him “I received from my master the Maggid, who received from his master the Baal Shem Tov, who received from his known teacher [Achiya Hashiloni].” Thus the custom dates back to Achiya Hashiloni who was one of the Sages listed as part of the continuity of the Torah Shebaal Peh. [Rambam Hakdama]