Skandapurana 6.3.85.88

6.3.85.88

hṛdayāntarjale jāpyā prāṇāyāmo'thavā nṛpa .
gāyatrī vaiṣṇavī caiva saurī śaivī yadṛcchayā .
te'pi pāpaiḥ pramucyanta ityevaṃ śaṅkaro'bravīt .. 85.88 ..

Deep in the water, one should chant [prayers] or perform breath control, O king; / the Vaiṣṇava Gāyatrī, or the solar, or the Śaiva one at will; / they too are freed from sins—thus indeed spoke Śaṅkara.