פירוש על עבודה זרה 87:4

The Talmud cites a baraita about the blood that runs off from the sacrifices in the Temple. This blood would flow into the brook of Kidron and the water/blood mixture was sold as fertilizer to farmers. This is proof that the brook of Kidron does have vegetation, which now is a proof for R. Yose, that one may nevertheless grind up an idol, just as Asa did The other rabbis would answer that the brook of Kidron has several areas. Asa would have ground the idol up in a place without vegetation, for otherwise this is prohibited.