Dear Sir,
Hope you are doing well !!
According to section 149, the income tax department has the powers to issue notice to taxpayers for seven years from the end of the financial year. So, this would mean that if you have filed ITR for FY 2018-19, then you must keep the related documents with you till the end of FY 2025-26.
It is advisable to keep the documents for seven years, however, this does not mean that once the specified period is over, you can throw away the required documents.
However, "According to the amendment made in Budget 2017, applicable with effect from AY 2017-18 (April 1, 2017), income tax officers can now ask details up to 10-year-old cases that involves large amounts of escaped income."