Srimad-Bhagavatam: Canto 9 - Chapter 1 - Verse 35

Sanskrit:

ज्येष्ठं मन्त्रद‍ृशं चक्रुस्त्वामन्वञ्चो वयं स्म हि ।विश्वामित्र: सुतानाह वीरवन्तो भविष्यथ ।ये मानं मेऽनुगृह्णन्तो वीरवन्तमकर्त माम् ॥ ३५ ॥

ITRANS:

jyeṣṭhaṁ mantra-dṛśaṁ cakrustvām anvañco vayaṁ sma hiviśvāmitraḥ sutān āhavīravanto bhaviṣyathaye mānaṁ me ’nugṛhṇantovīravantam akarta mām

Translation:

Thus the younger Madhucchandās accepted Śunaḥśepha as their eldest brother and told him, “We shall follow your orders.” Viśvāmitra then said to his obedient sons, “Because you have accepted Śunaḥśepha as your eldest brother, I am very satisfied. By accepting my order, you have made me a father of worthy sons, and therefore I bless all of you to become the fathers of sons also.”

Purport:

Of the one hundred sons, half disobeyed Viśvāmitra by not accepting Śunaḥśepha as their eldest brother, but the other half accepted his order. Therefore the father blessed the obedient sons to become the fathers of sons. Otherwise they too would have been cursed to be sonless mlecchas.