shomyo

Since shōmyō began as the chanting of Buddhist texts in India and went from there to China before coming to Japan, it is now sung in three different languages. Those songs sung in the ancient Indian dialect are called bonsan […], those in Chinese are called kansan, and the songs in Japanese are wasan. Because the Japanese adopted Chinese ideographs for their written language, giving them Japanese pronunciations, it is possible for them to sing Chinese songs with their own pronunciation. This form of shōmyō developed into a distinct style called kōshiki.

2000, William P. Malm, Traditional Japanese Music and Musical Instruments, page 67

Yet another type of lineage to transmit ideas related to hongaku thought was that of the performers of shōmyō, or Buddhist vocal music. Originating in India, shōmyō in medieval Japan comprised several types, including hymns of praise for the Buddha in transliterated Sanskrit; hymns in Chinese, including both translations of Sanskrit and those newly composed in China; singing of gāthās, or verses from sūtras; sung forms of the nembutsu, such as the inzei or “prolonged voice” nenbutsu established on Mt. Wu-t’ai and introduced from China by Ennin in the ninth century; chanting of the names of the Buddhas, set to music and performed at religious ceremonies; and hymns of praise composed in Japanese (wasan).

2003, Jacqueline I. Stone, Original Enlightenment and the Transformation of Medieval Japanese Buddhism, page 129

One of the earliest forms of Japanese Buddhist music is shomyo, derived from a Chinese adaptation of Indian Vedic chants and thought to have been elaborated in Japan in the 8th century by monks returning from China.

(Can we date this quote?), “Japan: Shomyo Buddhist Ritual - Dai Hannya Ceremony”, in Smithsonian Folkways Recordings