大般涅槃經義記 5.252

5.252

第四重明許驗試中，初命大仙求與共試，「譬如」已下明其須試，先喻後合，金須三試，苦行亦爾。「帝釋於」下現可畏形、說可畏食、催令速施示可畏事，是三試也。

In the fourth [part], which re-elucidates the agreement to go and test [him], first [Indra] addresses the Great Ṛṣi, asking to test him together. From "just as" onward, it explains the necessity of the test, first with an analogy and then with the application: gold must undergo three tests, and an ascetic is also like this. From "Śakra then" onward, manifesting a terrifying form, speaking of terrifying food, and urging him to make the offering swiftly to show a terrifying matter are the three tests.