https://elifesciences.org/articles/31257
For the original SARS, it's palm civets, identified in less than a year. (The link to bats wasn't discovered until much later, by Shi Zhengli; but the intermediate host is enough to feel pretty confident it's natural-origin.)
For SARS-CoV-2, we're still waiting for that intermediate host. That's the significance of the early pangolin papers; but as Alina Chan and many others have noted, those papers have significant data quality issues, and even the Chinese have pretty much abandoned the pangolins.