What he was chanting while carrying earth at the Trench
Al-Bara says the dust had covered the hair on his chest.
اللَّهُمَّ لَوْلاَ أَنْتَ مَا اهْتَدَيْنَا وَلاَ تَصَدَّقْنَا وَلاَ صَلَّيْنَا فَأَنْزِلَنْ سَكِينَةً عَلَيْنَا وَثَبِّتِ الأَقْدَامَ إِنْ لاَقَيْنَا
Allāhumma lawlā anta mā-htadaynā wa lā taṣaddaqnā wa lā ṣallaynā. Fa-anzilan sakīnatan ʿalaynā wa thabbiti-l-aqdāma in lāqaynā
“O Allah, were it not for You we would not have been guided, nor given in charity, nor prayed. So send down calm upon us, and hold our feet firm if we meet them.”
Sakīnah before firmness. Calm first, then the feet.
Where this comes from
A siege, a ditch being dug by hand, and the Prophet carrying earth with everyone else until he was covered in it. The lines are Abdullah ibn Rawahah's, and al-Bara says he was raising his voice with them.
The full narration
Narrated Al-Bara:I saw Allah's Messenger (ﷺ) on the day (of the battle) of the Trench carrying earth till the hair of his chest were covered with dust and he was a hairy man. He was reciting the following verses of `Abdullah (bin Rawaha): "O Allah, were it not for You, We would not have been guided, Nor would we have given in charity, nor prayed. So, bestow on us calmness, and when we meet the enemy. Then make our feet firm, for indeed, Yet if they want to put us in affliction, (i.e. want to fight against us) we would not (flee but withstand them)." The Prophet (ﷺ) used to raise his voice while reciting these verses. (See Hadith No. 432, Vol)
Source
Ṣaḥīḥ al-Bukhārī · 3034
- Agreed upon as authentic (al-Bukhārī / Muslim)