योगवासिष्ठः yogavāsiṣṭhaḥ - book-7, chapter-167, verse-21

इदं फेनो न किंचिद्वा बुद्बुदो वा न कश्चन ।
शून्यताम्भसि चिद्व्योम महार्णवमहोदरे ॥ २१ ॥

idaṃ pheno na kiṃcidvā budbudo vā na kaścana ,
śūnyatāmbhasi cidvyoma mahārṇavamahodare 21

21. We know nothing of the inanity of the vacuous soul, as to whether it is as the chasm in the foam or froth, or whether it is as the air in a bubble or spray; or whether it is as the gap amidst waves of the sea or what it is at all.