Subject: [{Package}] Some sources are not included in your package
Package: {Package}
Version: {Version}
user: lintian-maint@debian.org
usertags: source-is-missing
severity: serious
X-Debbugs-CC: ftpmaster@debian.org

Hi,

your package includes some files that seem to lack sources
in preferred forms of modification:

{list of files}

According to Debian Free Software Guidelines [1] (DFSG) #2:
 "The program must include source code, and must allow distribution 
  in source code as well as compiled form."

In some cases this could also constitute a license violation for some
copyleft licenses such as the GNU GPL. (While sometimes the licence
allows not to ship the source, the DFSG always mandates source code.)

In order to solve this problem, you could:
1. add the source files to "debian/missing-sources" directory.
2. repack the origin tarball and add the missing source files to it.

Both ways satisfy the requirement to ship all source code. The second option
might be preferable due to the following reasons [2]:
 - Upstream can do it too and you could even supply a patch to them, thus
   fulfilling our social contract [3], see particularly §2.
 - If source and non-source are in different locations, ftpmasters may
   miss the source and (needlessly) reject the package.
 - The source isn't duplicated in every .diff.gz/.debian.tar.* (though
   this only really matters for larger sources).

You could also ask debian-qa@lists.debian.org or #debian-qa for more
guidance.

[1] https://www.debian.org/social_contract.en.html#guidelines
[2] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=736873#8
[3] https://www.debian.org/social_contract