Al-Adaa’: It is the undertaking of the Waajib in its time that has been specified for it by the Shar’a.

Al-Qadaa’: The undertaking of the Waajib after the passing of the time specified for it by the Shar’a.

The Adaa’ Al-Waajib (The obligatory performance) in respect to its undertaking or performance is divided into two categories in regards to the time: Muqayyad (restricted) and Mutlaq (unrestricted).

1 - Al-Waajib Al-Muqayyad: It is what the Shaari’ has requested to be done by way of a Talab Jaazim (decisive request) within a specific time (frame). This is divided into two categories:

A – Al-Waajib Al-Muwassa’: That which the time for its performance is specified providing room or space for it and other than it from its same kind or type (Jins) to be performed within it.

This is that in which the specified time for its performance is in surplus of it (i.e. in surplus of the time needed to perform it). So Salaat uzh-Zhohr for example is a Waajib Muwassa’ as the time for its performance has been specified between the Zawaal of the sun from the meridian until the time when Salaat ul-‘Asr begins. Consequently, in this time period that has been specified for it the Mukallaf has the choice to undertake the Salaah in any part within it. The Waajib is fulfilled by the Mukallaf in all of the segments of time during the period and therefore the Waajib falls from him (i.e. he would have fulfilled it) by his performance of it within any time of its specified time period.

Consequently, if the Mukallaf was to delay the Salaah from its beginning or early time whilst he was resolved to perform it and then died before the passing of the time period without having performed it, he would not meet Allah Ta’Aalaa as someone who had been disobedient (in respect to that specific obligation). However, if the Mukallaf believed it most probable that he would die during the specified time period of the Salaah, like if he was to know the time of his execution for example, then he would be disobedient to Allah (swt) by delaying it from its earlier or beginning time. That is because in respect to the Waajib Al-Muwassa’ it must be most probable in the mind of the Mukallaf that he will undertake the obligation within its time period and if it is not most probable then it is not Halaal for him to delay it.

B – Al-Waajib Al-Mudayyaq (the narrow obligation in respect to time):

This is that which the time for its performance is specified whilst providing no room or space for other than it from its own kind or type (Jins).

This refers to the obligation that has a specific time for its performance without surplus or extra time and this is like the fasting of Ramadhaan as its time does not expand or provide room except for the performance of the obligatory fast within it.

2 – Al-Waajib Al-Mutlaq (the unrestricted obligation):

This is what the Shaari’ has requested to be done by a decisive request (Talab Jaazim) without having specified a specific time for its performance. This is like the Kaffaraat (expiations) and the Mutlaq Nudhoor (unrestricted vows). Or it is like the example of the Hajj which has been provided with a specific time for its performance within the year but has not compelled its performance to a specific year. The performance of these types of obligations are required from the Mukallaf if he is capable of undertaking them during his life whilst the obligation falls from him if he is unable to undertake them during his lifetime and there is no punishment due upon him as a result of that in the Aakhirah. That is because Allah does not burden a person above his capacity or capability. However, if the causes for its undertaking have been met and he views that he is most likely to pass away before its undertaking and yet does not undertake it, then he would be sinful.

Al-Qadaa’ refers to the undertaking of the Waajib after the passing of its time that has been specified for it by the Shar’a.

The Qadaa’ relates to the Waajib which is restricted (Muqayyad) to a specific time whether that time was Muwassa’ (was extended and had room) like the time for the Salaah or Mudayyaq (no extended room) like the fasting of Ramadhaan.

The Qadaa’ of the Waajib is obligatory upon the one who is capable. That is because the undertaking of the Waajib in its time represents a performance of what is obliged upon him and if the time passes without the person having undertaken the Waajib whilst he was capable of it then his responsibility would remain active and it is obligatory for him to fulfil it through the Qadaa’. The leaving of the Waajib that demands the performance of the Qadaa is of three types:

1 – That which the Mukallaf leaves deliberately:

If the Mukallaf leaves the performance of the Waajib intentionally (‘Amd) like the Salaah or Sawm then he is sinful and Al-Qadaa’ is obligatory upon him.

2 – That which the Mukallaf left out of forgetfulness:

If the Mukallaf leaves the performance of the Waajib due to forgetfulness (Sahw), the Qadaa’ becomes obligatory upon him but there is no sin upon him. The Messenger of Allah (saw) said:

If in this case the person does not perform the Qadaa’ for what he missed he would then be sinful.

3 – That which the Mukallaf leaves due to an excuse (‘Udhr):

If the Mukallaf leaves the performance of the Waajib dues to a Shar’iy ‘Udhr (excuse) that prevents its performance, then it is a duty for that person to make Qadaa’ for that action after the passing of that preventer (or excuse). That is like the Haa’id (menstruating woman) or the Nufasaa’ (women who are bleeding post birth) in respect to Ramadhaan. That is because the Shaari’ has given her a special permission not to fast and prevented her from fasting during the Haid and Nifaas whilst it is obligatory for her to make Qadaa’ for what she missed after she has become purified. As for the Salaah then Allah Ta’Aalaa has pardoned the Haa’id and the Nufasaa’ from making Qadaa’ for what was missed.

The Musaafir (traveller) and Mareed (sick person) must make Qadaa’ if they do not fast in Ramadhaan although the travel and sickness differ from the Haid (menstruation) and the Nifaas (post childbirth bleeding). That is because they are two excuses which do not prevent the person from performing the fast due to the Qawl of Allah Ta’Aalaa:

As for the one who fears death or a great harm due to the fasting then he will be disobedient for leaving the food due to its crime against the Rooh (i.e. body) which represents a Haqq (right) of Allah Ta’Aalaa in respect to him and therefore it is obligatory for him to break his fast or not fast (Iftaar).