AC said :

# Thank you for your submission. Unfortunately, we cannot publish this content as is, because you did not cite your sources. Please consult the citation examples within our Submission Guidelines for in-depth information on how and when to cite your sources within content.
# We encourage you to edit this content and resubmit for Upfront Payment consideration.

I have rewritten the article from an article directory. What Source should I Cite ???

How could anyone here possibly tell you what source to cite without knowing what your article was about?

Just think about it, go look up relevant info and add it in.

Elvis is right, you'll need to find the most relevent content to your article topic/content and add it as your sources. Usually, when they reject an article for not citing sources it's because it makes claims or has quotes within it that need to be backed up with some form of proof. When you rewrite your content, try to leave these parts of the article out or reword it so that it appears to be coming from your own "personal experience", rather than someone else's experience.

Also, like we've already talked about in length, article directories are a poor choice for drawing your original content from for AC.

I have re-written a mobile phone review.

You can also create your own source, by writing at least 1-2 similar articles and posting them to a blog you've created (under a different pen name). If you've set up an authoritative enough blog (not spammy looking), list it as your source, then submit your article to AC.