The affix ṇini comes after the verb yaj 'to sacrifice' with the sense of past time, when the word in composition is the Instrumental -3rd case.,
The anuvritti of णिनि and not of खश् is to be read into this sutra. As अग्निष्टोमयाजिन् 'who has sacrificed with Agnishtoma. Here Agnishtoma is the instrument for the attainment of the desired fruit.,