Comment by john-shaffer

  export LC_ALL=C
  nix-shell -I nixpkgs=https://github.com/NixOS/nixpkgs/archive/2322899a1fa85f6547004b2829af81e7b444f506.tar.gz -p openssh
  ssh -V
  OpenSSH_6.1p1, OpenSSL 1.0.0i 19 Apr 2012

Note that the first stable release of nixpkgs was in 2013.