Question: What are the cases that do not necessitate the repetition of salat?
ANSWER
Some of them are as follows:

[To carry out a salat within its prescribed time is called adaa. To carry it out after its prescribed time has ended is called qada (making it up). To carry it out again in order to make up for a defect or an error is called i’aadah (repeating).]

1. One who does not know the direction of the qibla must make an effort to locate it and then perform salat in the direction that one has decided to be right. After salat, if one finds out that it was not the right direction, one will not have to repeat it because one made an effort to locate the correct direction.

2. If the imam says that they performed the salat correctly while the jama’at says that they performed it wrongly, if the imam trusts himself or if he has a witness, the salat does not have to be repeated.

3. If a sahib-i tartib (a person who does not have any missed salat or has less than six) has a missed (qada) salat to make up, (s)he must perform the missed salat first and then perform the salat of the current time. If one forgets that one has a missed salat to make up as one begins the current salat or while performing it, the salat one performed is valid even if one remembers the missed salat after the current salat because it is an excuse to forget. One does not have to repeat it.

4. If one sees water after performing salat with tayammum because one could not find water, one does not have to repeat the salat.

5. If one is ill or when there is the danger that one’s possessions may be stolen or if the ship one is on board may sink or if there is the danger of a wild animal or of being seen by the enemy, one combines (jam’) two salats. If jam’ is impossible, one performs even a fard salat by standing toward any direction one can manage and does not perform it again later because one has not caused these excuses oneself, but they have happened beyond one’s control.

6. If the parts of one’s two hands and two feet that are obligatory to be washed in wudu’ have been amputated and if there is a wound on one’s face as well, one should perform salat without wudu’ because one cannot do tayammum, either. One does not have to repeat this salat afterward.

7. If impurity (najasat) splashes one one’s clothes and if one cannot locate the area smeared with it, it will be clean if one washes the area that one guesses to be the smeared one. If one discovers the correct area after salat, one does not have to repeat that salat.

8. One who cannot find anything besides a covering less than one-fourth of which is clean is permitted to perform salat with the covering or through gestures (ishaarah) sitting. However, with a covering one-fourth of which is clean, one has to perform it standing, in which case one will not repeat the salat later.

9. If a traveler can find water only for drinking within one mile, (s)he performs salat with the covering that has impurity on it, and (s)he does not perform it again later. [One statute mile is equivalent to 1,609 meters.]

10. If one doubts whether one performed the salat of the current time or not, one will not have to repeat it if the time for it has expired. (Se’adet-i Ebediyye)