Shiva Purana
तथा ब्रह्माहं सतनुस्तदंतं वीक्षितुं ययौ । भित्त्वा पातालनिलयं गत्वा दूरतरं हरिः १७ ।
Brahmā in the form of a swan went up in search of the top. Piercing through the netherworlds and going very far below, Viṣṇu could not see the root of the fiery column.
english translation
tathA brahmAhaM satanustadaMtaM vIkSituM yayau । bhittvA pAtAlanilayaM gatvA dUrataraM hariH 17 ।
hk transliteration by Sanscript