Scroll of Restoration

Restores 300 hit points and 150 mana of friendly non-mechanical units in an area 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.