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