俱舍論記 14.145

14.145

「為歸一佛僧一切佛僧耶」者，問。為復歸依一釋迦佛弟子僧耶？為歸一切三世諸佛弟子僧耶？佛之僧故，名曰佛僧。

Regarding the question, "Does one take refuge in the Saṃgha of one Buddha or of all Buddhas?": Is one taking refuge in the Saṃgha of disciples of one Buddha, Śākyamuni, or in the Saṃgha of disciples of all Buddhas of the three times? Because they are the Saṃgha of a Buddha, they are called the "Buddha's Saṃgha."