法華義疏 2.412

2.412

「八百弟子中有一人」者，第六、明彌勒本緣也。自上已來答彌勒問，明釋迦說法華經事竟。今此文別釋疑。疑云：彌勒既是補處，云何問文殊？是故今明過去本是師資，所以今有問答。文殊望彌勒是第十世師也。

As for "Among the eight hundred disciples there was one person": this is the sixth, clarifying Maitreya's former circumstances. From above down to here, answering Maitreya's question and clarifying the matter of Śākyamuni expounding the *Lotus Sūtra* is complete. Now this passage separately resolves a doubt. The doubt says: since Maitreya is already in the position of succession, why does he ask Mañjuśrī? Therefore it now clarifies that in the past they were originally master and disciple; this is why they now engage in questioning and answering. Looking from Maitreya's perspective, Mañjuśrī is his tenth-generation master.