In Tretā-yuga each leg of religion is gradually reduced by one quarter by the influence of the four pillars of irreligion — lying, violence, dissatisfaction and quarrel.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
त्रेतायां धर्मपादानां तुर्यांशो हीयते शनैः । अधर्मपादैरनृतहिंसासन्तोषविग्रहैः
tretāyāṃ dharmapādānāṃ turyāṃśo hīyate śanaiḥ | adharmapādairanṛtahiṃsāsantoṣavigrahaiḥ
SB 12.3.20