In 1150 (18 years old), Seishimaru moved to Bessho of Seiryu-ji Temple (in Sakamoto, Otsu city), was taught by Jigenbo Eiku Shonin, named Honen-bo Genku (used one Kanji character each from Genko and Eiko).
勢至丸・18歳（1150年）の時、青龍寺(大津市坂本)の別所に移り慈眼房叡空上人に師事して法然房源空（源光・叡空より一字ずつ名を貰った）と名のる。