ٱسْتَغْفِرْ لَهُمْ أَوْ لَا تَسْتَغْفِرْ لَهُمْ إِن تَسْتَغْفِرْ لَهُمْ سَبْعِينَ مَرَّةً فَلَن يَغْفِرَ ٱللَّهُ لَهُمْ ۚ ذَٰلِكَ بِأَنَّهُمْ كَفَرُوا۟ بِٱللَّهِ وَرَسُولِهِۦ ۗ وَٱللَّهُ لَا يَهْدِى ٱلْقَوْمَ ٱلْفَـٰسِقِينَ Qur’an Al-Tawba (9:80)Istaghfir lahum aw l a tastaghfir lahum in tastaghfir lahum sabAAeena marratan falan yaghfira All a hu lahum tha lika biannahum kafaroo bi A ll a hi warasoolihi wa A ll a hu l a yahdee alqawma alf a siqeen a
I.e., many times. In Arabic usage, the number "seventy" often stands for "many", just as "seven" is a synonym for "several" (see Lisan al-'Arab and Taj al-'Arus). It is evident from many authentic Traditions (recorded, among others, by Bukhari and Muslim) that the Prophet often prayed to God that He pardon his enemies.
I.e., "those who are so deeply rooted in their iniquity and in their insolent persistence in evildoing (tamarrud)... [that] they have lost all disposition for repentance and belief" (Manar X, 657).
An awful warning for those who actively oppose the Cause of Allah. The Holy Prophet was by nature full of mercy and forgiveness. He prayed for his enemies. But in such a case even his prayers are nullified by their attitude of rejecting Allah.