Reciting the Basmalah at the beginning of Soorat Baraa’ah (al-Tawbah); there is hardly any dispute among the scholars that doing this is makrooh (disliked).
Saalih said concerning some issues that he narrated from his father Ahmad (may Allaah have mercy on him): “I asked him about Soorat al-Anfaal and Soorat al-Tawbah, whether it is permissible for a man to separate them by saying Bismillaah il-Rahmaan il-Raheem. My father said: ‘With regard to the Qur’aan, reference should be made to what the companions of the Messenger of Allaah (peace and blessings of Allaah be upon him) were agreed on; nothing should be added to or taken away from that.’”
4 – Reciting it partway through Soorat al-Baraa’ah (al-Tawbah). The Qur’aan readers differed concerning that, as was narrated by Ibn Hajar al-Haythami in al-Fataawa al-Fiqhiyyah (1/52), and he said: “Among the leading Qur’aan readers, al-Sakhaawi said that there is no dispute that it is Sunnah to start with the Basmalah when one starts reading partway through this soorah [al-Tawbah], as he differentiated between starting at the beginning and starting in the middle, but his explanation was facile and was refuted by al-Ja’bari from among the Qur’aan readers. This is more likely (i.e., the view that it is makrooh is more likely to be correct), because the reason why the Basmalah should not be recited at the beginning (of al-Tawbah) is that it came with the sword (i.e., the command to fight the kuffaar) and it exposes the hypocrites and their foul deeds in a manner that is not unlike any other soorah, and this theme is repeated throughout Soorat al-Tawbah. Therefore it is not prescribed to recite the Basmalah even if one starts reciting partway through this soorah, just as it is not prescribed at the beginning, for the reasons we have established.”
See al-Adaab al-Shar’iyyah by Ibn Muflih, 2/325; al-Mawsoo’ah al-Fiqhiyyah, 13/253; al-Fataawa al-Fiqhiyyah al-Kubra, 1/52