Witches can't run away from their legacy, at least not the Halliwell sisters -- Prue (Shannen Doherty), Piper (Holly Marie Combs) and Phoebe (Alyssa Milano).
When The Seer foresees the demise of The Source by the Halliwell sisters, he decides to break the covenant between good and evil unleashing the ultimate power, the forbidden The Hollow
S4E12 44 min