Copying files with different extensions but one of them contains 'pattern'

I have several files in a directory and need to copy to a different location those which contain within the file -not within the name- a certain string.
After that, I also need to copy another set of files with matching names but different extensions to the same location as those which matched my previous search.

So far I know how to find the string using

grep 'pattern' *.ext1

and I tried to use

grep 'pattern' *.ext1 | xargs cp /newlocation

but to no avail.
Thank you