Garudapurana 3.29.11

3.29.11

maṇḍūkabhāryā gaṅgā tu saiva maṇḍūkinī smṛtā /
evaṃ catvārī rūpāṇi gaṅgāyā iti kirtitamam //

and as the frog's wife, that same Gaṅgā is remembered as Maṇḍūkinī. / Thus the four forms of the Gaṅgā are proclaimed.