三彌勒經疏 1.238

1.238

經曰「彌勒佛讚」以下，第七顯昔留化。謂曾彼惡世能修至心，故為傳化骨身留也。

From the sūtra passage stating, "The Buddha Maitreya praised," onward is the seventh, revealing his having remained to transform beings in the past. This means that having formerly been able to cultivate with utmost sincerity in that evil age, his bodily relics were left behind in order to transmit the teaching.