Shaggy Brown Bears in Western Plaguelands, at about 37, 79, and gather up as many of the bears as you can by using a non-damaging AoE (such as a warrior should/mass dispel) every few seconds to keep them from resetting, get like 30-40 of the bears, and once you have them all rounded up, just sit there, and it may take a few minutes, but they'll cast a buff on you called survival instincts, which increases your haste and size by 50% per buff (iirc), and can stack up to 31 times.
https://i.imgur.com/0OY4g.jpg