I am looking for example code for the MBILI board for sleep with minimum current consumption,
You should be able to reduce the standby current to as low as 300 microamps. This will depend on what modules you use for the wake interrupt. I believe the RTC based interrupt uses about 400 microamps.
Having an SD card inserted adds another 200 microamps.
It may be possible to reduce this further by trying to disable additional modules before entering sleep. However, most are already disabled when entering the powered down sleep mode.
There are two examples here, one using the an interrupt form the RTC another using the WDT:
Also it is possible to disconnect some of the on board LEDs using the solder jumpers. This will save additional power if those LEDs are lit.
See the Hardware Features tab of this page: