The community at r/ElCapitan and MacRumors Legacy Forums offers detailed walkthroughs and verified checksums for self-created ISOs. Stay safe, and enjoy the reliability of OS X 10.11—the last great cat before the macOS era fully took over.
Downloading pre-made ISOs from torrent sites or unknown file lockers is extremely dangerous. Macs are not immune to malware, and several “El Capitan ISO” downloads have been flagged for containing the Snake or Geost backdoors. Mac Os X El Capitan Iso Download