What documents need to be maintained for Income Tax

Since May 2023, I have been depositing hard cash around 50 thousand each month in my wife account. Sources of that amount is by doing freelance work such as data entry and taking tuition and other beautician works. As the amount is received by hard cash, and the total earning would come around only 5-6 lakhs each year is it mandatory to maintain any documents to prove the sources of income? Please advise