Vajrasuci (Siddhacarya Ghoshapada) 112

112

(jña) anyacca dūṣaṇaṃ bhavati| yadi mukhato111 jāto bhavati brāhmaṇo
brāhmaṇyāḥ kuta utpattiḥ| mukhādeveti ced? hanta tarhi bhavatāṃ bhaginīprasaṅgaḥ syāt| tathā gamyāgamyaṃ na sambhāvyate| tacca loke'tyantaviruddham
tasmādaniyataṃ brāhmaṇyam

(jña) And there is another fault: if the brāhmaṇa is born from the mouth, whence is the birth of the brāhmaṇa woman? If [you say] from the mouth indeed, alas, then there would be the contingency of [her being] your sister! Thus, what is permissible and impermissible for sexual union could not be determined, and that is utterly contrary to the ways of the world. Therefore, the condition of being a brāhmaṇa is variable.