وَلَقَدۡ كَانُواْ عَٰهَدُواْ ٱللَّهَ مِن قَبۡلُ لَا يُوَلُّونَ ٱلۡأَدۡبَٰرَۚ وَكَانَ عَهۡدُ ٱللَّهِ مَسۡـُٔولٗا

though they had already pledged to Allah before that they would not turn their backs [to flee], and pledges given to Allah are accountable.