分別功德論 4.5

4.5

凡乘虛者皆以神足，此比丘能行空如履地，是善肘比丘之所能也，故稱第一也。

All who ride the void do so by means of ṛddhi. That this monk could walk upon empty space as if treading on the ground was the capacity of the monk Subāhu, and therefore he is declared foremost.