Musnad Ahmad 33:99

Waki’ narrated to us, ‘Abd al-Wahid ibn Ayman narrated to us, from his father, from Jabir, who said: The Prophet, peace and blessings of Allah be upon him, and his companions remained for three days while they were digging the trench, not having tasted any food. They said: "O Messenger of Allah, there is a hard rock here in the mountain." The Messenger of Allah, peace and blessings of Allah be upon him, said: "Sprinkle it with water." So they sprinkled it. Then the Prophet, peace and blessings of Allah be upon him, came and took the pickaxe—or the shovel—and said: "In the name of Allah." He struck it three times, and it became a heap of sand that could be poured. Jabir said: I happened to glance, and behold, the Messenger of Allah, peace and blessings of Allah be upon him, had tied a stone against his stomach.