You can use rpm -qf /bin/ls to figure out what package your installed version belongs to:
[09:46:58] ~ $ rpm -qf /bin/ls
coreutils-8.5-7.fc14.i686
[09:47:01] ~ $
Update: Per your comment, the following should work if you want only the name of the package (I just got a chance to test):
[01:52:49] ~ $ rpm -qf /bin/ls --queryformat '%{NAME}\n'
coreutils
[01:52:52] ~ $
You can also use yum provides /bin/ls to get a list of all available repository packages that will provide the file:
[09:47:01] ~ $ yum provides /bin/ls
Loaded plugins: fastestmirror, langpacks, presto, refresh-packagekit
Adding en_US to language list
Loading mirror speeds from cached hostfile
* fedora: archive.linux.duke.edu
* rpmfusion-free: mirrors.tummy.com
* rpmfusion-free-updates: mirrors.tummy.com
* rpmfusion-nonfree: mirrors.tummy.com
* rpmfusion-nonfree-updates: mirrors.tummy.com
* updates: mirror.vcu.edu
coreutils-8.5-6.fc14.i686 : A set of basic GNU tools commonly used in shell
: scripts
Repo : fedora
Matched from:
Filename : /bin/ls
coreutils-8.5-7.fc14.i686 : A set of basic GNU tools commonly used in shell
: scripts
Repo : updates
Matched from:
Filename : /bin/ls
coreutils-8.5-7.fc14.i686 : A set of basic GNU tools commonly used in shell
: scripts
Repo : installed
Matched from:
Other : Provides-match: /bin/ls
[09:47:01] ~ $