your father can declare his undisclosed income under the income declaration scheme
2) Declaration can be made in respect of—
?any undisclosed income
?investment in any asset representing
undisclosed income
relating to any financial year upto 2015-16
3) Where undisclosed income invested in any
asset is declared under the Scheme & tax,
surcharge and penalty are duly paid on its fair
market value as on 01.06.2016 then, any
capital gains arising upon its sale in future
will be computed by adopting such fair market
value as on 01.06.2016 as the cost of
acquisition and the period of holding shall
also start from that date