Garudapurana 1.214.15

1.214.15

āpo tvantumasīti ca muñcantvavabhṛteti ca /
oṃ imaṃme varuṇa śrudhīhavamadyā ca mṛḍayatvā mavasyurācake //

and with “Waters, you are...”, “May they release...”, and “At the concluding bath...”:
“Oṃ, listen to this call of mine today, O Varuṇa, and show mercy; seeking your aid, I call on you.”