Unless the gift is over $17,000 you don't report it.
If it is, you would file a Form 709: United States Gift (and Generation-Skipping Transfer) Tax Return. You are not required to give info about the source/destination financial institutions involved.
You would need to download it from the IRS website, and mail in the paper form.
Here's more info about Reporting a Cash Gift.
**Say "Thanks" by clicking the thumb icon in a post
**Mark the post that answers your question by clicking on "Mark as Best Answer"