Income from home tution- no records kept

Hi,

One of my relative gives tution to the children in his locality going home to home. His total income for FY 16-17 was Rs. 3,20,000/- which he deposited in his savings account.

However due to unawareness he didnot kept any written records of his students and fees received from them. 

Now how should he proceed to file his ITR without any records of his income.? What if his case is later taken into scrutiny.?

Please advise.

Thank You.