Lord Viṣṇu — the Supreme Personality of Godhead, the spiritual master of all moving and nonmoving living beings, and the Supreme Soul of all — takes birth to protect the principles of religion and to relieve His saintly devotees from the reactions of material work.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
चराचरगुरोर्विष्णोरीश्वरस्याखिलात्मनः । धर्मत्राणाय साधूनां जन्मकर्मापनुत्तये
carācaragurorviṣṇorīśvarasyākhilātmanaḥ | dharmatrāṇāya sādhūnāṃ janmakarmāpanuttaye
SB 12.2.17