“Sanshō kasui (三生果遂)” is one of the names of the 20th vow of Amitābha Buddha used in the Jōdo sect, and points to the attinment of rebirth in the Pure Land after three reincarnations.
This idea is based on the “Sanshō ōjō (三生往生)” theory of the Tendai school popular during Hōnen’s lifetime.There are two varieties of this idea, one a Tendai interpretation, based on the teachings of the Smaller Sukhāvatīvyūha sūtra. The other is the so-called Nanto interpretation, related to the Nara schools. In Nara, there was discussion over transformational birth in the blissful land of Amitābha, an issue inherited from Chinese Pure Land teachings. Hōnen relied exclusively on the Tendai discussions, and Ryōchū 良忠 established the “Sanshō kasui” theory under this influence.