You do not need to submit any proof while e-filing your taxes. Keep it for your records and send when IRS requests it in the future.
If you do not have a Form W-2 for your foreign earned income, on the screen What Form(s) Was Foreign Income Reported
On ?check the third box A statement from my foreign employer (could be cash).
See attached screenshot
Here are the steps to enter your foreign earned income correctly in the TurboTax Premier online edition :
1. After sign into your account, select Take me to
my return
2. At the right upper corner, in the search box ,
type in foreign income and Enter
3. Select Jump to foreign income
4. Next screen, Did You Make Any Money
Outside the United States? answer Yes
5.
On
screen, What Form(s) Was Foreign Income Reported On ?check the
third box and continue to proceed
