That question raises a bunch of interpretive difficulties. You will find the expression sine qua non, which literally means "without which not," in some medieval writings about causation. For example, Aquinas rejects mere sine qua non causality as an adequate account of how the sacraments effect grace. In legal contexts today, that same expression denotes a simple counterfactual test for causation -- the "but for" test. One might try to interpret the phrase as meaning "indispensable" when Aquinas and other medievals use it and then deflate "indispensable" of its counterfactual content. However, if "indispensable" is supposed to lack counterfactual significance, then the same non-counterfactual reading could, I think, be taken with respect to that passage in Hume. I don't know if the idea shows up earlier. I wouldn't be surprised to find that it does.