What is the ruling on a husband enjoying his wife's underwear to quell his lust in her absence?

The Lawgiver (Allah) has restricted lawful enjoyment to one's wife and slave-women. Anything beyond that is considered an transgression against the sacred limits of Allah, as He states: "And those who guard their private parts. Except from their wives or those their right hands possess, for indeed, they will not be blamed. But whoever seeks beyond that, then those are the transgressors." As for the wife's clothing, if it is not clinging to her body, it is considered like any other garment, and enjoying it to relieve desire is not permissible.