To what extent is it preferable for a man to wash his wife [for burial]?

If the intention is to ask about the superiority of a husband washing his wife after her death, then the preponderant opinion is the permissibility of each spouse washing the other after death. No special virtue has been reported for a husband washing his wife, except that it might be more concealing for the deceased. However, if the intention is a husband washing his wife during her lifetime, there is no special virtue for that.