There is consensus among the schools that it is wajib to perform qada' of every obligatory salat omitted either intentionally, or on account of forgetfulness, ignorance or sleep, and that there is no qada’ for a woman for the prayers left during hayd and nifas, because salat is not wajib during these periods. The schools differ regarding one who is insane, unconscious or intoxicated.
The Hanafis state: Qada’ is wajib upon one who loses his senses by consuming a haram intoxicant, such as wine or something of its kind. As to someone insane or in a swoon, he is not required to perform salat in the following two situations: firstly, if the state of swoon or insanity continues for a period exceeding five salats (hence if it lasts for less than that period the person should perform its qada.'); secondly, if the recovery from insantiy or swoon does not occur at the time of salat (hence if he recovers and does not perform the salat its qada’ will be wajib upon him).
The Malikis are of the opinion that an unconscious or insane person has to perform qada’. An intoxicated person will perform qada’ if the cause of intoxication is the drinking of something haram; but if it is something halal (such as sour milk) there is no qada’ for it.
According to the Hanbalis, an unconscious person and one intoxicated by something haram will perform qada’, though an insane person is not required to do so.
The Shafi'is state: An insane person whose state of insanity extends over the entire period of salat will not perform its qada’. The same applies to one in a swoon or one intoxicated, provided he is not responsible for his state.
The Imamis consider it wajib for anyone who has consumed an intoxicant to perform qada’, irrespective of whether he drinks it knowingly or unknowingly, voluntarily or out of an exigency or under duress. As to an insane person and one in a swoon, they have no qada’ to perform.
The Hanafis and Imamis observe: A person who has omitted an obligatory salat will perform its qada’ exactly in the manner he would have performed it ada’. Hence if a person with an outstanding complete salat intends to perform it during journey, he should perform it completely, and one performing a qasr prayer as qada’ at home will perform it qasr. Similar is the rule respecting recital in a high or low voice. Hence if maghrib and 'isha’ prayers are performed qada’ during daytime, their recital will be loud, and in the qada’ of zuhr and 'asr prayers during night the recital will be in a low voice.
The Hanbalis and the Shafi'is state: The one who intends to perform the qada’ of a qasr prayer during journey will perform it qasr in accordance with the salat missed by him. But if he happens to be staying (hadr), it is wajib upon him to perform it complete as qada’. This was with respect to the number of rak’ahs.
As to its recital in a high or low voice, the Shafi'is say: The one who performs the qada’ of zuhr at night will recite in a loud voice and one performing qada’ of maghrib during daytime will do so in a low voice. The Hanbalis require all qada’ prayers to be recited in a low voice, irrespective of their being those that are recited in a high voice or low, and regardless of whether the qada’ is performed during daytime or at night, except where the person performing it is an imam and the salat is one which is recited in a high voice and it happens to be nighttime.
The schools, excepting the Shafi'i, concur that sequence should be maintained in the performance of the prayers missed. Thus the qada’ of one missed earlier will be performed before the qada’ of one missed later. Hence if maghrib and ‘isha’ prayers are missed, the former will be offered before the latter, as is the case while performing them ada'.
According to the Shafi'is, the maintaining of sequence in prayers missed is sunnah and not wajib. Hence the salat of a person who performs the ‘isha’ prayer before the maghrib prayer is valid.
There is a general consensus that appointing a proxy for carrying out prayers and fasts for a living person is not valid in any situation irrespective of whether he is capable or incapable of performing them himself. The Imamis state: It is valid to appoint a proxy for carrying out fasts and prayers on behalf of a dead person. The four Sunni schools observe: It is not valid in the case of a dead person, in the same manner as it is not valid for a living one.
The schools concur that appointing a proxy for Hajj is valid in the case of a living person provided he is incapable of performing it himself, and with greater reason in the case of a dead person. An exception are the Malikis who say: The appointing of a proxy, both for a living or a dead person, is of no consequence.
The Imamis are alone in observing that it is wajib for a child to perform the qada’ of the fasts and prayers left unperformed by its father. But they differ among themselves, and some of them state: It is wajib to perform all that which has been missed by the father, even if intentionally. Others say: It is necessary to perform the qada’ of only those acts which he has been unable to perform due to illness or some similar cause. There are others who observe: Nothing except that which has been missed by him during death-illness is to be performed as qada’ by the child. According to some others, the qada’ of the mother will also be performed by the child in the same manner as that of the father.