Bhagavatapurana 1.5.38

1.5.38

iti mūrtyabhidhānena mantramūrtim amūrtikam /
yajate yajñapuruṣaṃ sa samyag darśanaḥ pumān //

38. *He is, indeed, the man of right vision who thus worships the Lord of sacrifices, by mentioning the names of (and contemplating) the glorious forms of the Lord who has no form

other than what is contained in the Mantras, of whom Mantra is the form.