Both are considered passive forms. Use the one that sounds less awkward or which minimizes the emphasis on the less important object.
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hanuman_2000He was thrown the stone.Is the above one correct?No, because 'him' is not the indirect object in that structure. However, your sentence is OK as the passive of this one: He threw the stone to him.
hanuman_2000Both are the complement of preposition.But only #1 can be converted into an indirect object: He threw him the stone. You simply cannot ignore meaning when analyzing grammar.