分別功德論 1.12

1.12

佛不可思議者，昔時佛在靜室，諸梵天如恒邊沙來至佛所，欲知佛在何三昧，而不能知在何定中三昧。如是神足變現祕密之事，二乘所不能思議，豈況復凡庶。

As for the Buddha being incomprehensible: formerly, when the Buddha was in a quiet chamber, Brahmā devas as numerous as the sands of the Ganges came to the Buddha's place, wishing to know what samādhi the Buddha was in, yet they could not know which meditative absorption or samādhi he was in. Secret matters of ṛddhi transformations like this cannot be comprehended even by the two vehicles, how much less by ordinary mortals.