Its income to the business but not taxable. The credit should be to a revenue account (recommend separate so that your accountants ensure you do not pay tax on it).
Unfortunately if you have a company this amount is likely to be taxed when the retained profit is paid out to shareholders. So its not really tax free (unless you have an unusual franking account balance at the time which is not necessarily likely). If you operate a trust, partnership or sole trader this is not a problem – fully tax free no issues.