Explain the following statements with respect to a specific concept or convention along with its reasoning:

a. Near the end of the current year, a company required a customer to pay Rs.200,000 as a deposit for work that is to begin in the following year. At the end of the current year the company reported the Rs.200,000 as a liability on its balance sheet. Which accounting principle/guideline prevented the company from reporting the Rs.200,000 on its income statement for the current year?