The system procedure msdb.sys.sp_dbmmonitorresults calls msdb.sys.sp_dbmmonitorupdate. Within this procedure there is an insert into @results exec (@command). As such, you use insert into #mirroring_stats exec msdb..sp_dbmmonitorresults @database_name = 'NAV_Mirroring', @mode = 0, @update_table = 1.