It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that the Prophet (peace and blessings be upon him) said: "The Black Stone is one of the stones of Paradise, and there is nothing of Paradise on earth other than it. It was as white as an oryx, and had the filth of the Jahiliyyah not touched it, no one afflicted with an illness would touch it without being cured."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 11266