Where do I purchase flying?

[Jaquestiney-area-52]

Unlocking Flying in Battle for Azeroth: Part 1

I know most of you have this already, but it always seems to sneak up on a few people so we wanted to make sure everybody was aware of what Pathfinder Part 1 is and how to complete it before Part 2 (and flying) becomes available with Rise of Azshara.