Per IRS Publication 946 How to Depreciate Property, page 7:

Retired From Service

You stop depreciating property when you retire it from service, even if you have not fully recovered its cost or other basis. You retire property from service when you permanently withdraw it from use in a trade or business or from use in the production of income because of any of the following events.

• You sell or exchange the property. 
• You convert the property to personal use.
• You abandon the property.
• You transfer the property to a supplies or scrap account.
• The property is destroyed.

For additional information, please refer to IRS Publication 544 Sales and Other Dispositions of Assets.