Ali from Cairo

• WWizards of the Coast2004-10-04
  Official Ruling
  This effect does not apply to effects which reduce your life without doing damage.
• WWizards of the Coast2004-10-04
  Official Ruling
  This effect does not prevent damage, it prevents the damage from turning into loss of life. So the full damage is dealt (and abilities that trigger on damage being dealt still trigger), but the full loss of life is not applied.
• WWizards of the Coast2004-10-04
  Official Ruling
  The ability works up until Ali enters the graveyard, so if he takes lethal damage or is destroyed at the same time you take damage, the ability helps you. If the damage occurs after it goes to the graveyard, however, it is not affected by the Ali which is no longer on the battlefield.

Rulings via Scryfall

• WO
  Wizards of the Coast2013-08-05

  Ali from Cairo was restricted in vintage on August 5, 2013. The four-of card limits and the increase in deck size helped, but it didn't stop the degeneracy, so the next step was to further limit how many of a card players could play with. Restriction meant that only one copy of the card could be included in the deck. Source: https://magic.wizards.com/en/news/making-magic/twenty-things-were-going-kill-magic-2013-08-01