俱舍論記 6.169

6.169

「雖無經說至無經說耶」者，說一切有部言：雖現無經說無為能作因，亦無處遮，又多隱沒，云何定判無經說耶？

Regarding 'Although no sūtra states […] is there no sūtra stating it?': the Sarvāstivādins say: Although there is currently no sūtra stating that the unconditioned is a kāraṇa-hetu, neither is it precluded anywhere, and furthermore many [sūtras] have been lost; how can one definitively judge that no sūtra states it?