[mds]

The first time I remember hearing the phrase was in 2009 when Roberts flubbed the swearing in oath at Obama's inauguration. They later announced that the oath was administered again privately "out of an abundance of caution."

Was that the origin, or was it in use before that?

[hammock]

https://books.google.com/ngrams/graph?content=%22abundance+o...

[judge2020]

Earliest I found (in terms of books with a year next to them) is from 1689:

https://books.google.com/books?id=4zJWAAAAYAAJ&newbks=1&newb...

[richardfontana]

Specifically for "out of an abundance of caution", in Google Books there begin to be usages around 1911, based on a very quick search. As noted by someone else it's a pretty common phrase among American lawyers.

[Spooky23]

Usually it’s used by attorneys to explain actions that aren’t required by policy or law to demonstrate that actions were taken based on circumstances.

[gnicholas]

It's a common phrase among lawyers, at least.