Proof for short term capital gains in equity

Hi,

My employer has asked for declarations of capital gains or other income for current FY along with necessary proof to calculate tax liability for the remainder of the year.

I have some STCG through sale of listed equity shares and some other income through sale of debt mutual funds.

What is the proof that I can submit to show the actual gain in both these cases? Isn't a declaration alone enough? 

Thanks,

Nikhil Talreja