Bhagavatapurana 11.4.20.p3

11.4.20.p3

niḥkṣatriyām akṛta gāṃ ca triḥ-sapta-kṛtvo $ rāmas tu haihaya-kulāpyaya-bhārgavāgniḥ &

Rāma, indeed, the fire of the Bhṛgus for the destruction of the Haihaya clan, / rid the earth of kṣatriyas twenty-one times;