Quran 8:31 – Beheading Of Nadir Ibn-al- Hathir
According to tafseer of Qurtubi and Kathir of relevent verse, they write that this ayah refer to Nadir ibn-al-hathir who came from persia and learned their stories. When Prophet Mohammad saw recite Quran, he will say that he can give similar stories. This person was killed in aftermath of Badar. Badar has been termed as differentiating day between right and wrong. Hence, we can safely say, it was no blasphemy but the law of itmam e hujjah. You can read more detail of Itmam hujjah in following discussion Discussion 37972