The story about Shree Markandeya-Muni and his escape from death via Shree Vasudeva-Mantra in "Shree NaraSimha-Purana" chunks into several sub-stories, including the sub-story in which hell dwellers obtain Krishna-Sarupya-Mukti thanks to the very simple garland of Mantras dedicated to Bhagavan Shree Vishnu.
"Shree NaraSimha-Purana", 8.41 says कृष्णरूपधराः सर्वे दिव्यवस्त्रविभूषिताः - kRRiShNarUpadharAH sarve divyavastravibhUShitAH - "After reciting Vishnu-Mantras the hell dwellers had obtained Krishna-rupas in Shree Vishnu-Loka".
The below Sanskrit text is
