Mahabharata 13.109.1

युधिष्ठिर उवाच · yudhiṣṭhira uvāca

सर्वेषामेव वर्णानां म्लेच्छानां च पितामहउपवासे मतिरियं कारणं च न विद्महे

sarveṣāmeva varṇānāṃ mlecchānāṃ ca pitāmahaupavāse matiriyaṃ kāraṇaṃ ca na vidmahe

Our plain-language meaning of this verse is waiting for scholar review.