763. One should always offer Asr prayers after the Zuhr prayers, and the Isha prayers after the Maghrib prayers. If one intentionally offers Asr prayers before Zuhr prayers, or Isha prayers before Maghrib prayers, one's prayers would be void.
764. If a person starts namaz with the niyyat of Zuhr prayers, and during the prayers he recollects that he has already offered Zuhr prayers, he is not allowed to change the niyyat to the Asr prayers.He should abandon that namaz, and start Asr namaz. And the same rule applies to the Maghrib and the Isha namaz.
768. If while offering Isha prayers, a person doubts after reaching the Ruku of the 4th Rak'at, whether he has offered Maghrib prayers, he should complete the Isha Prayers. Thereafter, he should pray Maghrib.
769. If a person is praying a particular namaz again as a precaution, and during the prayers he recollects that he has not offered the preceding namaz, he cannot change niyyat to that prayers. For example, when offering the Asr prayers again as a measure of precaution, he recollects that he has not offered the Zuhr prayers, he cannot change niyyat to Zuhr prayers.
770. It is not permissible to change niyyat from Qadha to Ada (i.e. prayers which is offered within the prescribed time), nor from Mustahab to obligatory prayers.
771. If a person has sufficient time at his disposal to offer prayers within the time, he can, while offering the prayers, change niyyat to Qadha prayers, provided that it is possible to do so. For example, if he is offering Zuhr prayers, he can change to Qadha of dawn prayers, only when he has not entered the Ruku of the third Rak'at.