What is the ruling on the right of retrieval when purchased goods are mixed with other goods indistinguishably?

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If one purchases oil and mixes it with other oil, or purchases wheat and mixes it with wheat such that the two cannot be distinguished, the right of retrieval (right to take back the specific item) is nullified. The fundamental proof for nullification is that the specific original chattel is no longer found, which invalidates the right to retrieval, similar to when the item is destroyed. Furthermore, what is taken in exchange for the item is merely a substitute, giving the creditor no special right to it over other creditors, as in the case of the item's complete loss. The Prophet's saying, "Whoever finds his chattel intact in its original form," implies finding the actual physical item, as evidenced by cases where the item is found after the seller's ownership has ceased, or when purchased wood is used in construction or a purchased slave bears a child.