Sheikh Salman al-Oadah
Some commentators on the Qur’ân mention an answer to be read out loud after reciting the rhetorical question that is posed in the final verse of Sûrah al-Tîn. The verse reads: “Is not Allah the wisest of judges?” [Sûrah al-Tîn: 8]
The invocation they recommend is: “Indeed He is, and I am one of those who bear witness to it.” (Arabic: balâ, wa anâ `alâ dhâlika mi al-shâhidîn).
The evidence for this is a hadîth related from Abû Hurayrah that can be found in Sunan Abî Dâwûd (887) and Sunan al-Tirmidhî (3347).
However, this hadîth has a weak chain of transmission. Therefore, we do not recommend a person should to adhere to this wording, since it is not authentically established by the Sunnah. It is alright to do so on occasion, but is should not become a habitual practice.
The same can be said for the final verse of Sûrah al-Qiyâmah: “Is He not, then, able to give life to the dead?” [Sûrah al-Qiyâmah: 40]
It is narrated from one of the Companions used to say upon reading this verse: “Indeed, O Lord, indeed. Glory be to you. (Arabic: balâ, yâ Rabb, balâ, subhânak).
This can also be said on occasion, but should not be adhered to all the time.
And Allah knows best.
Source: Islam Today