To withdraw the mind and the senses from all unworthy objects and their duc concentration (upon higher objects) is the highest penance. That is the highest of all duties. Indeed, that is said to be the highest duty.
मनसश्चेन्द्रियाणां चाप्यैकाम्यं परमं तपः। तज्ज्यायः सर्वधर्मेभ्यः स धर्मः पर उच्यते॥