Ibn Hajar in his biographical dictionary Lisan al-Mizan:
#IbnSina, Abu Ali, the chief, I don't know of him narrating anything of knowledge. Even if he did it wouldn't be permissible to narrate from him as he is a Faylasuf in approach, Misguided, may God not be pleased with him.

الحسين بن عبد الله بن سيناء أبو علي الرئيس * ما أعلمه روى شيئا من العلم (1218) ولو روى لما حلت الرواية عنه لأنه فلسفي النحلة ضال لا رضي الله عنه...

He quotes Ibn Sina saying:
My father was from those that answered the call of the Egyptians, and afterwards was one of the Ismailiyya...
وكان أبى ممن أجاب داعي المصريين وكان يعد من الإسماعيلية

He quotes alHamawi from his alMilal Wal Nihal: The scholar have agreed that Ibn Sina believe in creation's eternity, denying physical resurrection (but not spiritual), and it's been transmitted that he said God does not know the minutiae in particular only with general knowledge

So the scholars of his time and after them whose statements are accepted, they are unequivocal about his disbelief due to holding to these beliefs which are in difference to Muslim belief.

وقد اتفق العلماء على أن ابن سيناء كان يقول بقدم العالم ونفى المعاد الجسماني ولا ينكر المعاد النفساني ونقل عنه انه قال إن الله لا يعلم الجزئيات بعلم جزئي بل بعلم كلي فقطع علماء زمانه ومن بعدهم من الأئمة ممن يعتبر قولهم بكفره ... من اجل اعتقاد هذه المسائل وانها خلاف اعتقاد المسلمين

He then relates that Abu Ubaid al-Jawzajani mentioned a story of him (Ibn Sina) becoming very ill, then repenting, giving Sadaqa, and righting wrongs.
فنقل إلى أصبهان واشتد ضعفه ثم اغتسل وتاب وتصدق ورد كثيرا من المظالم ولازم التلاوة ومات بهمدان

Later Ibn Hajar says: AlGhazali pronounced takfir on him unrestrictedly, While Ibn Sina in his explanations on some medicines said "It is as the companion of our Sharia said peace be upon him.

أطلق الغزالي وغيره القول بتكفير ابن سيناء وقال ابن سيناء في الكلام على بعض الأدوية هو كما قال صاحب شريعتنا صلى الله عليه وآله

End quotes from Ibn Hajar.
While IbnHajar relates this, it's important to remember that Ibn Sina's repentance from his atheism wouldnt suffice, he'd have to renounce his Ismaili beliefs as well to have been considered a Muslim at the end of his life. Allah knows best if he did.