Surah Al-Ahzab, ayah 15

33:15

وَلَقَدۡ كَانُواْ عَٰهَدُواْ ٱللَّهَ مِن قَبۡلُ لَا يُوَلُّونَ ٱلۡأَدۡبَٰرَۚ وَكَانَ عَهۡدُ ٱللَّهِ مَسۡـُٔولٗا ١٥

Walaqad kānū 'āhadullāha min qablu lā yuwallūnal-adbāra wakāna 'ahdullāhi mas'ūlā

And they had already promised Allāh before not to turn their backs [i.e., flee]. And ever is the promise to Allāh [that about which one will be] questioned.