Casting Multiple Times in a Round

Doc charges into battle against a Earth Grue--his plan is to use a swift action to cast Shield of Faith on Cat the Ranger and then cast Spiritual Weapon.

DM Alan rules that I can only cast once per round.

I admit that I have not read the D&D Next rules and that DM Alan is right, but I cannot find the ruling.

Can someone point me to this rule in the current D&D Next rules?