cash deposit during demonetization

my friend has a business and he is filing tax return and submitting sale tax as per his business norms for last 20 years. During demonitision , he deposited rs 17 lacs in his current account. His books are as per the norm and sale tax s paif accordingly. 3 days before, he got message from income tax dept for depositing this amount. Pls suggest how to respond for the same. Does he need to show his sale book to income tax dept ?