Section 148 of the Income Tax Act outlines the procedure for issuing a notice when income has escaped assessment. Here's a simplified breakdown:

1. Notice Requirement:

   • Before the Assessing Officer (AO) proceeds with assessing, reassessing, or recomputing under Section 147, a notice is served to the assessee.
   • This notice requests the assessee to file their income tax return (or that of any other person they are assessable for) for the previous year relevant to the assessment year.
   • The return should be filed in the prescribed form and verified as per the prescribed manner. The rest of the applicable provisions of the Act (like Section 139) will apply to this return.

2. Validity of Certain Notices (Provisos):

   • There are provisions to validate certain notices issued between October 1, 1991, and September 30, 2005 under Section 148.
   • If a return was filed during this period, and a notice under Section 143(2) was issued after a 12-month window but before the assessment time limit under Section 153, the notice would still be considered valid.
   • The second proviso further clarifies a similar validation if the notice under Section 143(2)(ii) was issued in a delayed manner within certain time limits.

3. Clarification:

   • The explanations added ensure that these validating provisions (in the first and second proviso) do not apply to returns filed on or after October 1, 2005 in response to a notice under this section.

4. Recording of Reasons:

   • Before issuing a notice, the AO is required to record reasons for their belief that income has escaped assessment.

This process ensures the taxpayer is notified and provided with an opportunity to file a return, and the AO's reasons for initiating reassessment are documented.