Musnad Ahmad 33:108

Waki' narrated to us, 'Abd al-Wahid ibn Ayman narrated to us, from his father, from Jabir, who said: "When the Prophet, peace and blessings of Allah be upon him, and his companions dug the trench, they were struck by severe hardship, to the point that the Prophet, peace and blessings of Allah be upon him, tied a stone over his stomach due to hunger."