If those cracks on the feet, where a lot of Vaseline has been applied, are very deep, that there is difficulty and harm in inserting water in them, then pouring water on top will be sufficient. It is not necessary to take it (Vaseline) out. 

However, if there is no difficulty in inserting water in the cracks, then wudhu and ghusl will not be valid due to the presence of the cream (Vaseline). Rather, it would be necessary to remove the cream (Vaseline), as much as possible, and pour water on it.

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للمفتي محمد أشرف الاشاعتي

Vol.1 Pg.91