Srimad-Bhagavatam: Canto 9 - Chapter 1 - Verse 33

Sanskrit:

ये मधुच्छन्दसो ज्येष्ठा: कुशलं मेनिरे न तत् ।अशपत् तान्मुनि: क्रुद्धो म्‍लेच्छा भवत दुर्जना: ॥ ३३ ॥

ITRANS:

ye madhucchandaso jyeṣṭhāḥkuśalaṁ menire na tataśapat tān muniḥ kruddhomlecchā bhavata durjanāḥ

Translation:

When requested by their father to accept Śunaḥśepha as the eldest son, the elder fifty of the Madhucchandās, the sons of Viśvāmitra, did not agree. Therefore Viśvāmitra, being angry, cursed them. “May all of you bad sons become mlecchas,” he said, “being opposed to the principles of Vedic culture.”

Purport:

In Vedic literature there are names like mleccha and yavana. The mlecchas are understood to be those who do not follow the Vedic principles. In former days, the mlecchas were fewer, and Viśvāmitra Muni cursed his sons to become mlecchas. But in the present age, Kali-yuga, there is no need of cursing, for people are automatically mlecchas. This is only the beginning of Kali-yuga, but at the end of Kali-yuga the entire population will consist of mlecchas because no one will follow the Vedic principles. At that time the incarnation Kalki will appear. Mleccha-nivaha-nidhane kalayasi karavālam. He will kill all the mlecchas indiscriminately with his sword.