法華義疏 11.154

11.154

「滿百千歲」者，神力一時未足希有，滿百千歲方是奇特。又是顯法久住故神力時長。

As for "completing a hundred thousand years": supernatural powers for a brief moment are not yet sufficiently rare; only when they complete a hundred thousand years are they extraordinary. Furthermore, this reveals that the Dharma will abide for a long time, and therefore the duration of the supernatural powers was long.