Atharvavedaparishishta 2.2.5

2.2.5

senāyā rakṣaṇe tasmāt svarāṣṭraparivṛddhaye | śāntyarthaṃ ca mahīpālo vṛṇuyād bhārgavaṃ gurum ||

Therefore, for the protection of the army, for the increase of his own realm, / and for the sake of propitiation, the ruler of the earth should choose a descendant of Bhṛgu as spiritual guide.