Scroll of Restoration

Fully restores the hit points and mana of all friendly non-mechanical units around your Hero.

Source
Illidan can find one in A Destiny of Flame and Sorrow, chapter 6 of the Warcraft III night elf campaign, Eternity's End.

Illidan, Kael, Lady Vashj and Akama can find one in Lord of Outland, chapter 6 of the Frozen Throne alliance campaign, Curse of the Blood Elves.