What is the ruling on a disbeliever participating in the burial, washing, and shrouding of a Muslim?

It is not permissible for a disbeliever to wash a Muslim, because washing is an act of worship, and a disbeliever is not qualified for it, nor can he form the correct intention. However, if a Muslim is present and intends the washing, and seeks the help of a disbeliever for assistance, such as bringing water, there is no harm in that.

It is permissible for a disbeliever to shroud and bury a Muslim, because it is not a condition for these actions that their doer be among those qualified for acts of drawing closer to Allah.