9:1
A (declaration) of immunity from Allah and His Messenger to those of the Pagans with whom ye have contracted mutual alliances:-
According to the commentary Bayan al-Qur’an, the verse declares a formal disavowal by God and His Messenger toward the idolaters of Arabia. It indicates that the existing treaties with the polytheists were annulled, except for those agreements specifically addressed in the verses that follow. The commentary also notes that this sūrah does not begin with the phrase Bismillāh al-Raḥmān al-Raḥīm, which appears at the beginning of other chapters of the Qur’an. This absence is explained by the report attributed to ʿAlī ibn Abī Ṭālib, who stated that the phrase Bismillāh signifies assurance of mercy and protection, whereas this sūrah was revealed in the context of a declaration of disavowal and confrontation toward those who had violated their covenants (Thanvi, 2007).
References:
Ahmad, Israr. (2012). Bayan ul Quran. Bayan Ul Quran – Dr. Israr Ahmed (English)