Vishnusmriti (Smritisandarbha) 98

98

nārāyaṇāya nama omiti vedamantraṃyo nityameva manasāpi samabhyasecca
pāpaiḥ pramucya parame tṛṣayātiviṣṇoḥsthānaṃ hi sarvamiti vedavido vadanti

Whoever constantly practices even with the mind this Vedic mantra, ‘Om, praise to Nārāyaṇa’, / freed from sins, goes to the supreme place of Viṣṇu; for ‘All is this,’ the knowers of the Veda say.