Hi @Lisa1509
So this is not somthing a host should be doing, (unless you've both already spoken about it and are both fine)
Refuse the request.
If the host can't host you, then they would have to get in touch with airbnb to cancel (and yes they would have penalties for that) but if you accept then you wont be able to canel the booking, you'll be stuck with a booking you don't want.
If you accept you'll be stuck with a 3 day booking, and trying to add on 1 night somewhere else (which is likely to cost more as you'll be paying cleaning fees twice)
If you refuse, then your booking has to be honored or you're entiled to a full refund if the host/airbnb cancels.
If you accept then try to cancel yourself, you loose the airbnb fees if you cancel more than 48 hours after the orginal booking was made.