Timatic (the visa system used by most airlines) does not mention any requirements to show details of accommodation.
Many countries will ask for details of accommodation on entry, generally as one of their multiple check to confirm you are a legitimate tourist, and that you will be staying in approved accommodation.
In your case, you will be able to show your airline ticket and/or boarding pass for your same-day outgoing flight, so showing accommodation details would not only be silly, but would actually be an indication they you were NOT intending to leave the country as planned, which would be far more of an issue!
If you are asked to provide your accommodation details in writing just put "In Transit". If you are asked verbally, just show your boarding pass. Either way, you'll be fine!
Note that citizens of some countries do require a visa to enter Mauritius. If you are from one of these countries you will require a visa to enter the country - even if only for 8 hours!