This worked for me:
M-x customize-group RET smartparens RET
Then use the Easy Customization interface to toggle Smartparens Global Mode
to "off" (nil), then choose to apply and save your changes. (The setting started in the "off" state for me, but smartparens was active anyway. I had to toggle it "on" and back "off" to disable it successfully.)
EDIT: I take it back; it worked temporarily. Smartparens is activated again upon starting a new session. Maybe this is an issue with Prelude?