Shiva Purana
प्रो हि प्रकृतिजातस्य संसारस्य महोदधेः । नवं नावांतरमिति प्रणवं वै विदुर्बुधाः ४ ।
The syllable Om means an excellent boat to cross the ocean of worldly existence. ॥ Pra=of the Prakṛti i.e. the world evolved out of it. Navam—Nāvāṃ Varam—an excellent boat॥
english translation
pro hi prakRtijAtasya saMsArasya mahodadheH । navaM nAvAMtaramiti praNavaM vai vidurbudhAH 4 ।
hk transliteration by Sanscript