妙法蓮華經玄義 7.139

7.139

雖無長久之本，若須用方便者，佛有延促劫智，能演七日為無量劫義（云云）。

Although there is no long-enduring original source, if there is a need to use expedient means, the Buddha possesses the wisdom to extend or compress kalpas, and is capable of expanding seven days into the meaning of immeasurable kalpas (and so forth).