﴿ وَلَقَدْ كَانُوا۟ عَٰهَدُوا۟ ٱللَّهَ مِن قَبْلُ لَا يُوَلُّونَ ٱلْأَدْبَٰرَ ۚ وَكَانَ عَهْدُ ٱللَّهِ مَسْـُٔولًۭا ﴾

“although ere that they had vowed before God that they would never turn their backs [on His message]: and a vow made to God must surely be answered for!”

Though they had assuredly pledged to God before that that they would not turn their backs to flee; and a pledge given to God must be answered for regarding whether it was fulfilled or not.