As per the following LINK, the Income Tax Department has issued Press Release on 31.07.2017 that for the purpose of e-filing return, it would be sufficient as of now to quote Aadhaar or acknowledgement No. for having applied for Aadhaar in e-filing website. The actual linking of PAN with Aadhaar can be done subsequently, but any time before 31st August, 2017.
It has however, been made clear that the returns will not be processed until the linkage of Aadhaar with PAN is done.
LINK:
https://www.incometaxindia.gov.in/Lists/Press%20Releases/Attachments/647/PressReleas_Extension-of-efiling-31-7-2017.pdf
