Your Aadhaar number is necessary when you file your income tax returns. However, if you have applied for an Aadhaar card, you must have an enrolment ID which is provided by the enrolment agency when you apply for the Aadhaar card. If you do not get the Aadhaar card at the time of filing your income tax returns, you can quote the enrolment ID in place of your Aadhaar number and file your taxes successfully.