Is it true that Ibn Hazm declared anyone who recites "Bismillahi ar-Rahmani ar-Rahim" (In the name of Allah, the Most Gracious, the Most Merciful) a disbeliever, believing that it is not a Quranic verse, and are there proofs that confirm this, and what is the validity of considering the Basmala an innovation (bid'ah) or an act of disbelief (kufr)?

Ibn Hazm did not say that counting the Basmala as a verse of Al-Fatiha is an act of disbelief. Rather, he considered the disagreement regarding affirming the Basmala and counting it as a verse to be permissible. Whoever recites according to the روایت that counts it as a verse must affirm it in prayer. And whoever recites according to the روایت that does not count it has the option. Ibn Hazm mentioned that the Qur’an was revealed in seven ahruf (modes of recitation), and all of them are true. Thus, the Basmala is a verse in one authentic recitation, and not so in another authentic recitation. This is similar to the presence or absence of certain words in different verses, varying with the different recitations.