What is the ruling on using stones (hijarah) for Istijmar (purification by dry means)?

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The majority opinion among scholars holds that water is the primary means, but there is a narration stating that only stones suffice. Abu Bakr chose the latter view, which is also the school of Dawud, arguing that the command to use stones implies obligation, and since the text specified stones for a matter where concession was granted, one must adhere strictly to them, similar to the restriction regarding soil in Tayammum. The evidence for using materials equivalent to stones is derived from the Prophet's command to use three stones that do not contain excrement, implying the validity of stones and that which holds the same quality, excluding excrement.