Whatever result was obtained in Satya-yuga by meditating on Viṣṇu, in Tretā-yuga by performing sacrifices, and in Dvāpara-yuga by serving the Lord’s lotus feet can be obtained in Kali-yuga simply by chanting the Hare Kṛṣṇa mahā-mantra.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
कृते यद्ध्यायतो विष्णुं त्रेतायां यजतो मखैः । द्वापरे परिचर्यायां कलौ तद्धरिकीर्तनात्
kṛte yaddhyāyato viṣṇuṃ tretāyāṃ yajato makhaiḥ | dvāpare paricaryāyāṃ kalau taddharikīrtanāt
SB 12.3.52