Sayyiduna Abdullah bin Amr (may Allah be pleased with them both) said: When the Prophet (peace and blessings be upon him) ordered the trench to be dug and a trench was dug around Madinah, the people said: O Messenger of Allah! We have come across a rock which we cannot dig through. The Prophet (peace and blessings be upon him) stood up, and we stood up with him (peace and blessings be upon him). When he (peace and blessings be upon him) reached it, he took the pickaxe, struck it a blow and said the takbir, and I heard a resounding crash the like of which I had never heard before. He (peace and blessings be upon him) said: "Persia has been conquered." Then he struck a second blow and said the takbir, and I heard a resounding crash the like of which I had never heard before. He (peace and blessings be upon him) said: "Rome has been conquered." Then he struck a third blow and said the takbir, and I heard a resounding crash the like of which I had never heard before. He (peace and blessings be upon him) said: "Allah has brought Himyar as helpers and supporters."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 13651