योगवासिष्ठः yogavāsiṣṭhaḥ - book-7, chapter-41, verse-17

सत्यं सत्ये स्थितं शान्तं सर्गात्मन्यात्मनि स्वयम् ।
आकाशकोशसदृशं शिलाजठरसंनिभम् ॥ १७ ॥

satyaṃ satye sthitaṃ śāntaṃ sargātmanyātmani svayam ,
ākāśakośasadṛśaṃ śilājaṭharasaṃnibham 17

17. Viewed in the reality of Brahma, the unreal world becomes a reality; it seems then to be as tranquil as the nature of God, and the creation is seen in himself till at last all is lost in the womb of a void—vacuum, as it were hid in the hollow cavern of a rock.