The prayers which should be performed in sequence
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.
765. If a person somehow becomes sure while offering the Asr prayers that he has not offered the Zuhr prayers, and changes niyyat to the Zuhr prayers, but later he recollects that he has infact already offered the Zuhr prayers, he can again revert to Asr, and complete the prayers, provided that he has not performed important parts like Ruku', Sajdah or any other part with the niyyat of Zuhr, otherwise his prayers will be void, and he has to offer all over again.
766. If, while offering the Asr prayers, a man doubts whether he has offered the Zuhr prayers, he should complete his namaz with the same niyyat of Asr, and then pray Zuhr. However, if the time is so short, that that the sun would set by the time he finishes the prayers, and there would be no time left even for one Rak'at, then it is not necessary to pray Zuhr namaz as Qadha.
767. If, while offering the Isha prayers, a man doubts whether he has offered Maghrib prayers, he should complete the namaz with the same niyyat of Isha. But if the time is short, and he will not be able to perform even one Rak'at after completion of Isha, it is not necessary to pray Maghrib as Qadha.
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, if the time for it is still available (i.e. if it is not Qadha).
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.