We said to the Messenger of Allah ﷺ on the day of the Trench, when exhaustion had overcome us, "Is there something we can say?"He replied, "Say, 'O Allah, cover our weaknesses and calm our fears.'"Then Allah routed them with the wind.
قلنا لرسول الله ﷺ يوم الخندق وقد بلغ منا الجهد: هل من شيء نقوله؟ قال: قولوا: اللهم استر عوراتنا، وآمن روعاتنا. قال: فهزم الله بالريح.
Bazzar reported it in Kashf Astar (3119) from Muhammad bin Muthanna, who said, Abu Amir Abdul-Malik bin Amr narrated to us, who said, Zubayr bin Abdullah narrated to us, and it is said, Ibn Ruhayma, from the people of Madinah, from Rabih bin Abdul-Rahman bin Abu Saeed, from his father, from his grandfather, and so he mentioned it.Its chain of transmission is hasan, and the discussion of it is set out in detail in the section on the military campaigns.