Rule 702.103d

When casting a spell bestowed, only its characteristics as modified by the bestow ability are evaluated to determine if it can be cast. Example: Aether Storm is an enchantment with the ability “Creature spells can’t be cast.” This effect doesn’t stop a creature card with bestow from being cast bestowed. Example: Garruk’s Horde says, in part, “You may cast creature spells from the top of your library.” If you control Garruk’s Horde and the top card of your library is a creature card with bestow, you can cast it as a creature spell, but you can’t cast it bestowed.