The Law Code of Nārada v12.114

Nāradasmṛti v12.114

anantaraḥ smṛtaḥ sūto brāhmaṇyāṃ kṣatriyāt sutaḥ /
māgadhāyogavau tadvad dvī putrau vaiśyaśūdrayoḥ //