ZJ,
Adding to Josh's reply...
You can create a sales invoice by selecting the type of the fixed asset on the line. This lets you invoice an asset to a customer. The disposal of a fixed asset through a sales invoice or sales order works in the same manner as the disposal through a FA G/L journal. Let me walk thru the steps of Disposing a Whole Fixed Asset from a Sales Invoice:
1. Go to a Sales Invoice.
2. Click New to create a new sales invoice.
3. Press ENTER to have the program fill in the invoice number automatically.
4. In the Sell-to-Customer No. field, enter your Customer.
5. In the Posting Date and Document Date fields, enter your dates.
6. When you receive a warning about a Credit Limit check, click Yes, if this is active.
7. On the Lines FastTab, click the Type field, and then select Fixed Asset.
8. Select the No. field, and then select the asset.
9. Type “1” in the Quantity field. No more than one asset for each sales line can be sold.
10. In the Unit Price Excl. VAT field, enter the net sales price.
11. MAKE SURE you have the column 'Depr. until FA Posting Date' visible. Add if missing. When visible, check box.
12. Open Sales Invoice Statistic to view the sales statistics for this invoice.
13. Click OK to close the Sales Invoice Statistics window.
14. Click Post, to post the invoice.
NOTE: Make sure any Dimensions you want set are entered before posting.
NOTE: Before performing a Disposal, make sure that in the FA Posting Groups window, for the related posting group(s), you set up all your Disposal Account columns. To open the FA Posting Groups window, in the search box, enter FA Posting Groups.

Hope this helps.
Thanks,
Steve