What is the authenticity of the mentioned hadith, and what is the meaning of Abu Bakr's saying: "Thus we were, then hearts hardened"? Is the explanation that it means "they became strong and tranquil through the knowledge of God" correct, or is Al-Alusi's explanation that "the first generation of Companions would weep out of fear of God when verses were recited to them, and that those who came after them had their hearts hardened" more correct?

The saying attributed to Abu Bakr al-Siddiq, "Thus we were, then hearts hardened," is not authentically established. It has been reported with disconnected chains of transmission from Abu Salih and Amr ibn Murrah. Even if it were authentic, it would be from the perspective of humility and admonition, not a description of his state; because hardness of heart means the loss of tenderness and submissiveness within it, which the Qur'an condemned in several places. Abu Bakr, however, was known for the tenderness of his heart and his frequent weeping when reciting the Qur'an. As for interpreting "hardness" as strength and tranquility in the knowledge of Allah, this is a weak interpretation that contradicts the language, the apparent meaning of the Sharia, and the state of the Companions.