Challenge Hawkmaster Nurong, and then defeat him in combat at Shado-Pan Garrison in Townlong Steppes.
You've really been building up respect with the Shado-Pan, <name>. Nurong's interested in trying out his skills against you. The good news is, if you win, I'll allow him to go with you on your missions. The bad news is, I really don't think you'll win.