Title: If the Moment Ever Comes
Author: somuchust
Rating: NC-17
Pairing(s): Sam/Dean
Warnings: NSFW, Wincest, genderswap (girl!Sam), sex, alcohol, some language  
Spoilers: /

Summary: A spell turns Sam into a girl. Dean doesn't recognize him, and Sam doesn't want to tell him quite yet.

Here at AO3.