Reference for Gittin 105:21
והאמר רבא מי חטאת
Now if you maintain that damage which is invisible is legally accounted as damage, then he should be liable also before the earthly court? — He raised the objection and he himself answered it, thus: [The work referred to in the case of] the heifer [was] that he brought it into the stall with the intention of letting it suck and then threshing with it;<span class="x" onmousemove="('comment',' I.e., he had not yet done with it any work for which the earthly court could punish him, but he is punished by heaven for his intention. ');"><sup>19</sup></span> in the case of the water [the work referred to was] that he balanced weights against it.<span class="x" onmousemove="('comment',' We assume that the exact weight of the water was known to him. In this case he had done no actual work with the water. ');"><sup>20</sup></span> But has not Raba said that water of purification