Ramayana
ततस्त्वमपि दुर्धर्षात्तस्माद्भावात्सनातनात् । रक्षार्थं सर्वभूतानां विष्णुत्वमुपजग्मिवान् ॥ 7-104-9 ॥
Then you too, for the protection of all beings, took on the state of Vishnu, arising from that unassailable, eternal Being.
english translation