As I discuss in this question, by far the most popular school of Hindu philosophy is the Vedanta school, which bases its tenets on the doctrines laid out in the Brahma Sutras, a work by the sage Vyasa that summarizes and systematizes the philosophical teachings of the Upanishads. (You can read the Brahma Sutras here.) But the Vedanta school didn't always have the dominant position in Hindu philosophy; before the time of Adi Shankaracharya the dominant school of Hindu philosophy was the Purva Mimamsa school, which I discuss here. In contrast to the Vedanta school which is devoted to analyzing the Jnana Kanda of the Vedas, i.e. the Upanishads, Purva Mimamsa focuses on analyzing the Karma Kanda of the Vedas, i.e. the Samhitas and Brahmanas.
Now unlike the Vedanta school, which believes that Brahman dispenses rewards and punishments based on people's actions, the Purva Mimamsa school believed that actions create an Apurva or unseen entity, and then that Apurva later brings about a positive or negative result for the person who did the action. In this excerpt from Shabara's commentary on the Purva Mimamsa Sutras, the defining text of the Purva Mimamsa school, Shabara argues that Apurvas must exist, because actions no longer exist after they're finished so they cannot directly lead to a result:
If it be argued that "on the strength of the declaration of a certain result following from a certain sacrificer, it may be presumed that the act of sacrifice itself does not perish", the answer is that such a presumption cannot be right; because of the Act itself we do not perceive any other form[.]
Now in this excerpt from Kumarila Bhatta's Tantra Vartika, a subcommentary on part of Shabara's Bhashya, Kumarila Bhatta responds to the objection that Shabara's statement that actions are not perceived is incorrect, since actions are by their very nature perceptible to the senses. Kumarila Bhatta clarifies that Shabara simply means that we do not perceive the action at the time when it bears fruit, not that the action is never perceived:
[In reply to this theory, the Bhashya says - 'we do not perceive any shape of the Action', and against this it is urged that] "This assertion is not quite correct, because Action has been distinctly mentioned as perceptible by the Senses, under Sutra 'Rupashabdavibhagacha'." ... What is meant by the assertion that no shape of Action is perceived is that we are not cognizant of any such form of Actions that would enable them to function at a future time, and as for the impermanent forms of Actions that are perceived, these can be of no use in the bringing about of the final Result.
I'm interested in the part in bold. My question is, what scripture contains the Sutra "Rupashabdavibhagacha"? This Sutra apparently signifies that action is perceptible to the senses.
In principle this Sutra could be from the Purva Mimamsa Sutras, but I don't think the Purva Mimamsa Sutras contain any such statement. So I'm thinking that it's most likely from one of the other Darshana Sutras, like the Nyaya Sutras, Vaisheshika Sutras, etc.