وَلَقَدْ كَانُوا عَاهَدُوا اللَّهَ مِن قَبْلُ لَا يُوَلُّونَ الْأَدْبَارَ وَكَانَ عَهْدُ اللَّهِ مَسْؤُولًا
[33:15]
And certainly they had made a covenant with Allah before, that) they would not turn (their) backs; and Allah's covenant shall be inquired of.
And yet they had already covenanted with Allah not to turn their backs, and a covenant with Allah must (surely) be answered for.
And verily they had already sworn unto Allah that they would not turn their backs (to the foe). An oath to Allah must be answered for.