Sarvadarshanasangraha 13.46

13.46

tasmād yaś cobhayoḥ samo doṣo na tenaikaś codyo bhavatīti nyāyād varṇānām eva vācakatvopapattau nātiriktasphoṭakalpanāvakalpata iti cet

Therefore, as there is a well-known rule that when the same fault attaches to both sides of an argument it cannot be urged against one alone, we maintain that the hypothesis of the existence of a separate thing called sphoṭa is unnecessary, as we have proved that it is the letters which express the word's meaning [your arguments against our view having been shown to be irrelevant].