Devibhagavatapurana 3.18.13

3.18.13

vāgbījasya japātsiddhistasyā eṣāpyupasthitā |
sopi dhyānaparo'tyantaṃ jajāpa mantramuttamam ||

S’as’ikalâ, too, began to recite slowly the root mantra of Sarasvatî and therefore her love towards this prince held out signs of success.
Once engaged in meditation on that excellent root mantra on Kâma, and, while repeatedly reciting it mentally, he got in a dream the vision of that Ever Full, the World Mother Ambikâ, that cannot be expressed in words, the Vaisnavî S’akti and capable to bestow all wealth and property.