Taxpayer who wants to link their Aadhaar number with PAN is required to send SMS to 567678 or 56161 in following format:
UIDPAN<space><12 digit Aadhaar><space><10 digit PAN>
Example of SMS to 567678 or 56161:
UIDPAN 111122223333 AAAPA9999Q
Aadhaar number will be linked with PAN if name and date of birth of taxpayer is identical to Aadhaar and PAN.
Source: Income Tax India’s Official Website