Srimad-Bhagavatam: Canto 9 - Chapter 1 - Verse 3
एते क्षेत्रप्रसूता वै पुनस्त्वाङ्गिरसा: स्मृता: ।रथीतराणां प्रवरा: क्षेत्रोपेता द्विजातय: ॥ ३ ॥
ete kṣetra-prasūtā vaipunas tv āṅgirasāḥ smṛtāḥrathītarāṇāṁ pravarāḥkṣetropetā dvi-jātayaḥ
Having been born from the womb of Rathītara’s wife, all these sons were known as the dynasty of Rathītara, but because they were born from the semen of Aṅgirā, they were also known as the dynasty of Aṅgirā. Among all the progeny of Rathītara, these sons were the most prominent because, owing to their birth, they were considered brāhmaṇas.
Śrīla Viśvanātha Cakravartī Ṭhākura gives the meaning of dvi-jātayaḥ as “mixed caste,” indicating a mixture of brāhmaṇa and kṣatriya.