Accounting for advance retainers received

[CuriousEL]

Hi All

After a lengthy discussion with fellow mates something simple has now turned to complicated

My issue is how do you properly account for advance retainers in your accounting books. My client needs an INVOICE for Retainer in order to make a payment but this is not a sale. Because it's an unearned income it's recorded as a liability.
I want to EXCLUDE the Retainer from Income but how do I do this??