Mahabharata 1.158.19

तथा पितॄन्वैतरणी दुस्तरा पापकर्मभिःगङ्गा भवति गन्धर्व यथा द्वैपायनोऽब्रवीत्

tathā pitṝnvaitaraṇī dustarā pāpakarmabhiḥgaṅgā bhavati gandharva yathā dvaipāyano'bravīt

Our plain-language meaning of this verse is waiting for scholar review.