Mahabharata 13.16.29

देवासुरमनुष्याणां यच्च गुह्यं सनातनम्गुहायां निहितं ब्रह्म दुर्विज्ञेयं सुरैरपि

devāsuramanuṣyāṇāṃ yacca guhyaṃ sanātanamguhāyāṃ nihitaṃ brahma durvijñeyaṃ surairapi

Our plain-language meaning of this verse is waiting for scholar review.