As dagger and bow are the only two ways to kill a sleeping target quickly before it becomes an assault rather then murder, I wonder.

Is there a bound dagger spell in the game? Simply answer YES or NO, please! Don't want any real spoilers.

Is it possible without cheating or turning down difficulty level to be able to MURDER people with Magic as they sleep, Destruction without getting an "assault" thing on your log?
Yes or no?

I've only encountered Bound Battleaxe and Bound Sword, but I'm only level 27 at the moment.

EDIT: UESP says only Bound Sword, Axe, and Bow. You can still be a sneaky assassin with a bound bow. Also, modding in more bound weapons shouldn't be that hard. All a modder would have to do is make a spell that summons a weightless Daedric Dagger and applies the shader effect to it.

No bound dagger.

Bound bow is your best option. There's also an Illusion perk which makes spells fom all schools silent that you may find useful.

But when I unleash a huge Fireball on my foe in a town, when he is sleeping.. like.. will it be silent with the park from Illusion star tree?

the casting of the fireball makes noise and the impact makes noise i think but if it one shots, it shouldn't count as assault. just make sure the spell doesn't wake them up when cast. i've found that bound weapons are extremely loud. I've been walls between bandits and they hear me recast my bound sword