Tax assessment notices cannot be issued after three years, if the estimated concealment of income is below Rs 50 lakh
An income-tax notice cannot be issued if three years have passed since the end of the relevant assessment year. However, if there is evidence of concealment of income of at least Rs 50 lakh, a notice can be issued beyond three years but within 10 years of the end of the relevant assessment year.
Source: moneycontrol.com