Now we come to those 6 wajib acts which are ghayr rukn. i.e.. if anyone of them is added or left out intentionally, the prayer would be invalid (batil); but if it is added or left out by mistake or unintentionally, no harm will come to the prayer (except that some remedial actions are prescribed in certain cases).
It is obligatory to recite Surah al-Hamd and then any other Surah (with certain conditions) in the first two rak'ats of every prayer (except Salat al-mayyit), and to recite either Tasbihat al-‘Arba’ah (Subhanallahi wal-hamdu lillahi wa la ilaha illal-lahu, wallahu akbar) or Surah al-Hamd in the third and fourth rak'ats.
Certain things are wajib in the qir'at;-
1. Correct pronouncement of the words and letters, so as the similar letters may be distinguished from each other in a correct way. This needs practice and training.
2. Fatha. kasra, damma, tashdid, madd, and jazm should be pronounced correctly ..
3. When stopping on a word, its last I’rab should be replaced by jazm, compulsorily. Likewise, when two words are joined, the first word's I’rab should not be omitted.
4. Bismillahir-Rahmanir Rahim should be recited before every Surah except Surah al-Bara'ah, because it.is part of every Surah (except al-Bara'ah).
5. The four Surahs in which wajib sajadahs occur, should not be recited in obligatory Salat. But it is allowed in mustahab prayer. If he recited that Surah in a mustahab prayer, he must do sajdah, just after reciting the verse of sajdah, then stand up and finish the Surah and prayer as usual. If he recited that Surah in wajib prayer by mistake, or if he heard someone else reciting the verse of sajdah (when the hearer is praying wajib prayer), he should do the sajdah after prayer. It is better to do sajdah, by gesture of head only during prayer itself, and then to do sajdah after finishing the prayer.
6. Reciting the Surahs and Tasbihat al-‘Arba’ah with tama’ninat.
7. A man should recite al-Hamd and Surah loudly in the first two rak'ats of Subh, Maghrib and ‘Isha; and in a whisper in the first two rak'ats of Zuhr and ‘Asr. 'Loudly' does not mean shouting, which many people resort to behind the prayer leader. If someone prays so loudly that it may be said that he is 'shouting' his prayer is batil (invalid). The whisper should be audible to the person himself. The qir'at in the 3rd and 4th rak'ats of every prayer should be in a whisper.
A woman should recite her prayers in a whisper, though she is allowed to pray loudly (where a man should pray loudly) when there is no danger that any ghayr mahram is nearby who may hear her voice. If someone intentionally prays loudly in place of "whispering", or vice-versa, his prayer is batil (invalid).
8. Reciting the Surah al-Hamd and Surah with tartib (in the sequence which is prescribed).
9. Muwalaat in the qir'at.
10. Surah al-Duha' and Surah Alam Nashrah are one Surah.
Likewise, Surah al-Fil and Surah al-Qur’aysh are one Surah. If one of the Surahs is recited, the other one also should be recited.
11. A man who has started reciting any Surah after al-Hamd, may change to another Surah so long as he has not reached to the exact middle of that Surah. If he has, on the other hand, recited half that Surah, he is not allowed to change it. But he cannot leave Surah al-Ikhlas or Surah al-Kafirun even if he has just recited Bismillahir Rahmanir-Rahim with the intention of these Surahs.
If he forgets any word or verse from the Surah which he is reciting, he may leave the Surah and start another one, even if he has already recited more than half, or even if it is Surah al-Ikhlas or Surah al-Kafirun.
12. It is allowed to recite the Surah by looking into the Qur’an in Prayer; but it is not good and one should not resort to it except in emergency when there is no time to learn by heart, nor is there any Salat al-jama’ah (congregational prayer) to join.