deb http://cdn-fastly.deb.debian.org/debian/ jessie main
deb-src http://cdn-fastly.deb.debian.org/debian/ jessie main

deb http://security.debian.org/ jessie/updates main
deb-src http://security.debian.org/ jessie/updates main

deb http://archive.debian.org/debian jessie-backports main
deb-src http://archive.debian.org/debian jessie-backports main

(without the jessie-updates repository).

You’ll also need to disable validity checks in /etc/apt/apt.conf (which will apply to all repositories):

Acquire::Check-Valid-Until "false";