My dear King, as a pot containing liquor cannot be purified even if washed in the waters of many rivers, nondevotees cannot be purified by processes of atonement even if they perform them very well.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
प्रायश्चित्तानि चीर्णानि नारायणपराङ्मुखम् । न निष्पुनन्ति राजेन्द्र सुराकुम्भमिवापगाः
prāyaścittāni cīrṇāni nārāyaṇaparāṅmukham | na niṣpunanti rājendra surākumbhamivāpagāḥ
SB 6.1.18