What is the authenticity of the hadith that prescribes for the reciter of the Quran to say "Allahu Akbar" (God is Most Great) upon completing each surah, starting from Surat Ad-Duha?

The hadiths about reciting Takbir during recitation cannot be authentically attributed to the Prophet, peace and blessings be upon him. However, this is the recitation of Ibn Kathir al-Makki, through the narrations of al-Bazzi and Qunbul.

Al-Qurtubi mentioned that the reciter pronounces Takbir in al-Bazzi’s narration from Ibn Kathir, and that Mujahid narrated it from Ibn Abbas, from Ubayy ibn Ka'b, from the Prophet, peace and blessings be upon him, that he used to pronounce Takbir from Surat Ad-Duha until the end of the Qur'an, with a short pause between the end of the surah and the Takbir.

Al-Hakim mentioned in "Al-Mustadrak" that Abdullah ibn Kathir informed him, on the authority of Ubayy ibn Ka'b, that the Messenger of Allah, peace and blessings be upon him, commanded him to do so. He described it as an authentic hadith that they (Bukhari and Muslim) did not include.

Takbir has also been reported from Qunbul's narration. For more information, one can refer to "An-Nashr ala al-Qira'at al-Ashr" and the commentaries on Ash-Shatibiyyah.