Washing a corpse, before burial, is also a part of the religious
customs and traditions promoted by the previous prophets of God. Although
it suffices to thoroughly pour water over the dead body, yet in view
of the extraordinary importance of cleanliness and physical cleansing,
the corpse should be washed as thoroughly as possible. The Prophet
(pbuh) is reported to have said:

Wash he with water and jujube leaves three,
five or even more times, if you would. And the last time you wash
her, mix some camphor in the water as well.
According to another narrative, the Prophet (pbuh)
is reported to have said:
Wash her in odd numbers, three, five or
seven times. Start with her right side and wash those parts first,
which are washed during ablution for prayers.