Mmm I checked and it's quite probable I'm wrong. Ooops sorry.
After Turtle lost and shaman flee you need speak again with the turtle (or it's forced) and at end of this dialog you'll receive two scrolls but not necessary Magic Spring unlike what I believed. I hope you have your save game to check it by doing again the turtle battle and see the reward.
I'm not fully sure but I retract what I said.
EDIT: Shame on me, I checked with a warrior savegame, replayed the battle, ask to the turtle, agree to give blood, make the pact with the turtle, nothing. I cannot believe it. I go checking again.