Plutarch, De Stoicorum repugnantiis
Goodwin, Ed.

Moreover, having said in his book of Exhortations, [p. 452] that the having carnal commerce with our mothers, daughters, or sisters, the eating forbidden food, and the going from a woman's bed or a dead carcass to the temple, have been without reason blamed, he affirms, that we ought for these things to have a regard to the brute beasts, and from what is done by them conclude that none of these is absurd or contrary to Nature; for that the comparisons of other animals are fitly made for this purpose, to show that neither their coupling, bringing-forth, nor dying in the temples pollutes the Divinity. Yet he again in his Fifth Book of Nature says, that Hesiod rightly forbids the making water into rivers and fountains, and that we should rather abstain from doing this against any altar. or statue of the Gods; and that it is not to be admitted for an argument, that dogs, asses, and young children do it, who have no discretion or consideration of such things. It is therefore absurd to say in one place, that the savage example of irrational animals is fit to be considered, and in another, that it is unreasonable to allege it.