debian 8 apt
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";