Charmed (1998)

S6E16 The Courtship of Wyatt's Father

Gideon strikes a pact with the Darklighters to eliminate Leo, but the plan backfires, transporting Leo and Piper to the Ghostly plane. This mishap leads Phoebe and Paige to think they’ve lost both of them for good. At the same time, Chris starts to fade away and discloses that he needs to be conceived by the end of the night, or he will cease to exist entirely.