Quran 8:31 – Beheading Of Nadir Ibn-al- Hathir
Kindly always give reference to the verse which you refer to. If you are talking about verse 8:31, it was not revealed in the background of behaeading. Actually, Quran is refering to the Challenge of meccans (including Nadir ibn-al-hathir) if Quran is from Allah why there is no azab and these are stories of previous people.