I have a message in Facebook that I want to send to another Facebook friend. How do I go about doing that?
If it is an extensive discussion and it cannot be taken off of Facebook (mail/skype etc) then use Groups as temporary message boards. The current flaw (last time I checked, this could have been removed by now) in groups allows you to add friends without having them accept. You can then start the message there and those who have been invited will receive a notification. Use with caution this can be used for malicious purposes.
Otherwise it is not possible without just copy/pasting the message.
Source - How can I forward a message or add someone to a message thread?