Musnad Ahmad 658:222

Muhammad ibn Ja‘far narrated to us, ‘Awf narrated to us, from Maymun Abu ‘Abd Allah, from al-Bara’ ibn ‘Azib, who said: The Messenger of Allah (may Allah bless him and grant him peace) commanded us to dig the trench. He said: A rock appeared to us in a place in the trench, upon which the pickaxes would not take effect. He said: They complained about it to the Messenger of Allah (may Allah bless him and grant him peace). The Messenger of Allah (may Allah bless him and grant him peace) came. ‘Awf said: And I think he said: He placed his garment, then descended to the rock and took the pickaxe. He said: "In the name of Allah," and struck a blow, breaking a third of the stone. He said: "Allah is the Greatest! I have been given the keys of Ash-Sham. By Allah, I can see its red palaces from this place of mine." Then he said: "In the name of Allah," and struck another, breaking a third of the stone. He said: "Allah is the Greatest! I have been given the keys of Persia. By Allah, I can see al-Mada'in, and I can see its white palace from this place of mine." Then he said: "In the name of Allah," and struck another blow, and dislodged the remainder of the stone. He said: "Allah is the Greatest! I have been given the keys of Yemen. By Allah, I can see the gates of Sana'a from this place of mine."