Ability to cast a specific spell, must the spell be prepared or only known?

[Kraschong]

Hallo, I seek clarification for this feat

Channeling Force (Combat)

You distill your channeled energy into a sheen of force that surrounds your weapon for a limited time.

Prerequisite(s): Ability to cast at least one force spell, channel energy class feature.

Benefit: A swift action, you can expend one use of channel energy to grant your weapon attacks a bonus on damage rolls equal to the number of dice of your channel energy. This extra damage is force damage. This lasts for your next three weapon attacks or until the end of combat, whichever comes first.

My question: Must the PC prepare a force spell or needs he only to know a spell?

[Starglim]

He has the ability to cast a spell with the force descriptor if it is among the spells he can prepare, or if he knows it as a spontaneous caster. He doesn't have to have it prepared or to have a spell slot of that level available, to use this feat.

[Jeff Morse]

^^^agree. So clerics can get it at 3rd level.oracles 5th i guess after adding spiritual weapon to spells known. Unless there is a first level spell now. Too many books to search

[Kraschong]

Thank you.