Bring the Bank Voucher to Karus in the bank of Orgrimmar.
[player], we could not have gotten this far without you. The time will come soon, no doubt, when I'll ask for your help against the silithid once more. We must absorb what we have learned in Un'Goro; I fear that my assumptions that the silithid originated from Un'Goro are now wrong... that indeed there is a far stronger presence somewhere.
Take this note to Karus at the bank. He'll give you something from my vault that should be viewed as a token of my gratitude. Thank you for your assistance, mighty [class].