Is it from the Sunnah to say, ‘Subhana Rabbi Al-A'la’ when one hears Surah Al-A'la being recited? Please give a reference or hadith. And what about saying, ‘Balaa’ at the end of Surah At-Teen.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah and that Muhammad is His slave and Messenger.

It is permissible, or rather recommended, for the reciter of the Quran to praise Allaah when he recites a verse in which there is praise such as the verse mentioned. Huthayfah ibn al-Yamaan narrated:

“I prayed with the Prophet one night and he started reciting Soorah Al-Baqarah. [I thought that he would bow at the end of the soorah, but he proceeded on.] Then he started Soorah Al-Nisa' until he completed it. [I thought that he would bow at the end of the soorah, but he proceeded on.] He then started Aal-‘Imraan and recited leisurely. When he recited a verse that referred to the praise of Allaah, he praised Him, when he recited a verse in which there is a supplication, he supplicated Allaah, and when he recited a verse in which there is seeking refuge with Allaah, he sought refuge with Allaah…” [Muslim]

The listener in this case is like the reciter, especially if he is not praying. Imaam An-Nawawi said:

“Ash-Shaafi’i and the scholars of our School said, 'It is recommended for the reciter, regardless of whether he is in prayer or outside the prayer, when he recites a verse in which mercy is mentioned, to ask Allaah for His Mercy; or a verse in which punishment is mentioned, to seek refuge with Allaah from His Punishment; or a verse of praise, to praise Allaah; or a verse in which Allaah cites an example, to ponder over it.' Our scholars said, 'This is desirable for the imaam and the person led in prayer as well as for the person praying alone.'”

Also, Sharh ‘Umdatul-Ahkaam by Ibn Jibreen reads, “As regards if you are outside the prayer, whether you are a reciter or a listener, then this is desirable, as this is asking for goodness and seeking refuge in Allaah from evil.” For more benefit, please refer to fatwa 91554.

As for the second part of the question: Al-Haakim reported from Abu Hurayrah that when the Prophet recited {Is not that [Creator] Able to give life to the dead?} [Quran 75:40], he said, “Bala (Yes, indeed);” and when he recited: {Is not Allaah the most just of judges?} [Quran 95:8], he said, “Bala.” Al-Haakim said, “The chain of narrators of this hadeeth is authentic,” and ath-Thahabi agreed with him on this.

Allaah knows best.