Nyāya Sūtras 151.4

151.4

yad upalabhyate tad asti, yan nopalabhyate tan nāsti, ity anupalambhātmakam asad iti vyavasthitam/ upalabdhyabhāvaś cānupalabdhir iti seyam abhāvatvān nopalabhyate/ sac ca khalv āvaraṇaṃ tasyopalabdhyā bhavitavyaṃ na copalabhyate tasmān nāstīti/

What is apprehended exists; what is not apprehended does not exist: thus what has the nature of non-apprehending is determined to be non-existent. And non-apprehension is the absence of apprehension; thus, being an absence, it is not apprehended. An obstruction, on the other hand, being an existent thing, would necessarily be apprehended, and it is not apprehended; therefore, it does not exist.