You could go for presumptive taxation u/s 44AD since you are not having any books of accounts nor any evidence of income. The activity of driving taxi on hire basis is a business that gets covered under section 44AD.
In that case, you may have to pay tax on 8% of your Gross receipts received/ receivable during the year & you dont have to maintain any records for the taxi income.
If the 4Lakhs mentioned above was your gross receipts, then the assessee may have to disclose 32,000 (ie., 8% of 4 Lakhs) as his/her income. Eventually the assessee could file a NIL income tax return under ITR-4S, provided the (8% amount + other income) does not exceed basic exemption limits.
If the 4 Lakhs mentioned was your profits (Taxi income - Expenses), then you may have to get the figure of total TAXI Income received during the year. The 8% of such income would be deemed to be your income. The assessee may file a return after including his/her other sources of income.
(Other views & suggestions are invited)