In ancient times, nenbutsu of Amida Buddha was preached as a representative of Shobutsugenzenzanmai (various forms of the Buddha appearing in meditation) in the "Hanju Zanmai-kyo Sutra" (sutra of the meditation to behold the Buddhas), and this became the basis of jogyo zanmai (constantly walking samadhi) in the Tendai sect.
古くは『般舟三昧経』に説かれる諸仏現前三昧の代表として阿弥陀仏の念仏が説かれ、これが天台宗の常行三昧のよりどころとなった。