There are two books called NOTHING BUT THE NIGHT, and that sounds like a quote from something but I can't think what.
Is it from a poem?
There is a poem by Raif Butler(?) but I don't think it's the source of the title.
There is at least one movie with that title.
There's one by Housman. A review of one of the books (by Bill Pronzini) cites this as the source of the title.
A. E. Housman (1859–1936). A Shropshire Lad. 1896.
LX. Now hollow fires burn out to black
NOW hollow fires burn out to black,
And lights are guttering low:
Square your shoulders, lift your pack,
And leave your friends and go.
Oh never fear, man, nought’s to dread, 5
Look not left nor right:
In all the endless road you tread
There’s nothing but the night.
Thank you, Pam! That must be it!
There's a John Blackburn novel called NOTHING BUT THE NIGHT, which was made into a movie called NOTHING BUT THE NIGHT, which was also released as THE DEVIL'S UNDEAD (despite the fact that there's no devil in the story and no undead people). There's also a more recent detective novel with the same title.