Musnad Abu Ya'la al-Mawsili 106:32

Wahb ibn Baqiyyah narrated to us, Khalid narrated to us, from ‘Awf, from Abu ‘Abd Allah Maymun, from al-Bara’ who said: The Messenger of Allah (may Allah bless him and grant him peace) ordered the digging of the trench. He said: A rock appeared to us that the pickaxes could not penetrate. They complained about that to the Prophet (may Allah bless him and grant him peace). He said: So he took the pickaxe. He said: And I think he said he laid down his garment, then he struck a blow and said, "In the name of Allah," and broke a third of the rock. Then he said, "Allah is the Greatest! I have been given the keys of Ash-Sham. Indeed, I am looking at its red palaces from this place of mine." Then he said, "In the name of Allah," and struck another blow and broke a third of it. He said, "Allah is the Greatest! I have been given the keys of Persia. By Allah, I am looking at al-Mada'in and its white palace from this place of mine." Then he said, "In the name of Allah," and struck another blow and broke the remainder of the rock. He said, "Allah is the Greatest! I have been given the keys of Yemen. By Allah, I am looking at the gates of San‘a from this place of mine."