I hope its a kind of gift received in cash from any relative or on occassion of your's friends' marriage.. If not so, the assessee may be in trouble as it may be difficult to prove it as non-taxable..In such a situation, I think either you can advise your friend (i) to revise his / her ITR by including it as it is or by claiming some expenditures , if possible, under appropriate "head of income "or by showing it as income from some "eligible business" as per sec-44AD & declaring 8% of turnover / gross receipts as "income" (if all the provisions of Sec-44AD applicable) & pay taxes accordingly, provided he / she has filed his/ her ITR by due date in A.Y. 2014-15 or (ii) by using some possible unfair means, which I would neither discuss nor like to advise you in this paltform.
Besides, as far as the interest on Rs.13 lakhs is concerned, it will be taxable either in the hands of "first account holder" or "that individual's account" who has higher interest income (provided both the joint holder has individual savings account), if it cannot be proved that the specific amount actually belongs to the specific jointholder, as then only it will be possible to tax interest incomes proportionately.
Requesting experts of CCI to give their valuable suggestions on this issue...