13.  Un-explained investments, etc., deemed to be income:-

(1)  Where,

(a)  any sum is found to be credited in the books of an assessee maintained for any income year; or

(aa) the assessee is found to have made any investment or is found to be the owner of any money or valuable article, in any year; or

(b)  the assessee is found to have made any investment in any income year which is not recorded in the books of account maintained for that income year or is not shown in the wealth statement or return of wealth furnished under section 58 in respect of that year; or

(c)  the assessee is found in respect of any income year to be the owner of any money or valuable article which is not recorded in the books of account, if any, maintained by him or is not shown by him in any wealth statement or return of wealth furnished under section 58 in respect of that year; or

(d)  the assessee has made investment in any income year or is found in respect of any such year to be the owner of any valuable article and the Deputy Commissioner finds that the amount expended on making such investment or in acquiring such valuable article exceeds the amount recorded in this behalf in the books of account maintained by him or shown in the wealth statement or return of wealth furnished under section 58 in respect of that year; or

(e)    an assessee has, during any income year, incurred any expenditure, and the assessee offers no explanation about the nature and source of such sum, investment, acquisition of the money or valuable article, excess amount or the money from which the expenditure was met, as the case may be, or the explanation offered by him is not, in the opinion of the Deputy Commissioner, satisfactory, the sum so credited, the value of the investment, the money or the value of the article, the excess amount or the amount of the expenditure, as the case may be, shall be deemed to be the income of the assesses of such income year chargeable to tax under this Ordinance:

Provided that, where any act referred to in clauses (a) to (e) is discovered after the assessment of income of the income year to which the said act relates has been made, the income chargeable to tax under this section shall be included in the total income of the income year relevant to the assessment year in which the said discovery is made:

Provided further that in cases referred to in clauses (aa) to (e) such income shall not be chargeable to tax unless approval of the Inspecting Additional Commissioner has been obtained.

(2)   Where the value of any investment or article referred to in clause (aa), (b), (c) or (d), or the amount of expenditure referred to in clause (e) of sub-section (1) is, in the opinion of the Deputy Commissioner, too low, the Deputy Commissioner may determine, after giving a reasonable opportunity to the assessee of being heard, a reasonable value or the amount thereof, as the case may be, and all the provisions of sub-section (1) shall have effect accordingly.

(3)  The Central Board of Revenue may by rules provide for the determination of the value of any property or article for the purposes of this section.