And they had already promised Allah before not to turn their backs (33:15)

Almuntakhab Fi Tafsir Alquran Alkarim

Yet they had already given their solemn promise to Allah never to defect, desert or flee the enemy. They failed to realize that an engagement entered into with Allah is indeed an immense responsibility

Tafseer Tafheem-ul-Quran by Syed Abu-al-A'la Maududi

(33:15) They had earlier covenanted with Allah that they would not turn their backs in flight. And a covenant made with Allah must needs be answered for. *27

And they had already promised Allah before not to turn their backs meaning

*27) That is, "They had felt regret at the weakness they had shown on the occasion of the Battle of Uhud and pledged to Allah that they would compensate for their error in any trial that they would confront in the future. But Allah cannot be deceived by empty words. He puts to one or the other test everyone who makes a pledge with Him so that his sincerity of intention or otherwise is found out. Therefore, just after two years of the Battle of Uhud, He made them confront an even more serious danger and discovered how far they were sincere in their pledge."
 

And they had already promised Allah before not to turn their backs meaning in Urdu

ان لوگوں نے اس سے پہلے اللہ سے عہد کیا تھا کہ یہ پیٹھ نہ پھیریں گے، اور اللہ سے کیے ہوئے عہد کی باز پرس تو ہونی ہی تھی