Please Help: INCOME TAX

ONE OF OUR CLIENT SHOWN RS. 4.05 LACS.AS COMMISSION RECEIVED FROM DIFFERENT PARTIES IN HIS ITR WITH OTHER BUSINESS INCOME AND PAY THE I. TAX. HIS CASE IS SELECTED FOR LIMITED SCRUTINY "CASH DEPOSIT". HE HAD NOT MAINTAINED PARTY WISE COMMISSION DETAILS. THE ITO DISALLOWED MY COMMISSION INCOME AS UNEXPLAINED CASH RECEIVED. WHAT ARE THE OPTIONS WE HAVE. PLS SUGGEST.