宋高僧傳 16.43

16.43

系曰：楚師明律，時號宗主者何？通曰：「律有三宗，礪、素、宣是歟。宗各有主，故云也。」觀夫是名也，豈無稽古乎？通曰：「『宗主』二字，出《阿含經》也。」

In appraisal: Master Chu elucidated the vinaya and was called lineage master at the time; why was this? In explanation: 'There are three traditions of the vinaya: Li, Su, and Xuan. Each tradition has its lineage master, hence the term.' Looking at this title, could it be without ancient precedent? In explanation: 'The two characters zongzhu (lineage master) appear in the Āgama sūtras.'