What is the Hadith of the Ifk (Slander), and is it related to Surat At-Tawbah and the absence of the Basmala at its beginning?

The story of the Ifk (slander) is mentioned in Surat An-Nur, and Abdullah ibn Ubayy ibn Salul was its chief instigator. Allah Almighty says concerning it: "Indeed, those who came with the slander are a group among you. Do not think it bad for you; rather, it is good for you. For every person among them is what he earned of sin, and he who took the major share of it, for him is a tremendous punishment." As for Surat At-Tawbah, it speaks about the hypocrites. The reason for not writing the Basmala at the beginning of Surat At-Tawbah is either that the recitation of the beginning of the surah was abrogated, or that it was revealed with the sword and punishment while the Basmala implies mercy, or that it is a continuation of Surat Al-Anfal, and for this reason, the Companions left a gap in the Mus'haf to indicate its beginning.