I got a job and I asked someone I know for a reference and they said they would but they haven't given me their contact details

I know they might be busy but I need to give my reference to the job, I asked yesterday night and they said yes, so I asked for their email but they haven't gotten back to me.

I need to give the company my reference, I want to be able to do it as soon as possible. Is there a polite way of messaging them again to ask or is it just rude because they are doing me a favor?