Call to undefined method Illuminate\Auth\GenericUser::save()

after i login i tried to update my user profile via form in UsersController. heres the code:

public function update(Request $request)
    {
        $user = Auth::user();
            $user->first_name = $request->first_name;
            $user->last_name = $request->last_name;
            $user->username = $request->username;
            $user->email = $request->email;
            $user->phone_no = $request->phone_no;
            $user->division_id = $request->division_id;
            $user->district_id = $request->district_id;
            $user->street_address = $request->street_address;
            $user->shipping_address = $request->shipping_address;
            if ( !empty($request->password) ) {
                $user->password = Hash::make($request->password);
            }
            $user->save();
            session()->flash('success','user profile has been updated');
            return back();
    }

'''

but get this error on $user->save(); my User model is untouched. can anyone spot the error please?

via Chebli Mohamed