● It is preferable to fast consecutively when making up missed fasts if they were missed due to a valid excuse.

● However, if the fasts were missed without a valid excuse, then fasting consecutively is obligatory, because making up the missed fasts in this case must be done immediately.

Separating the makeup fasts goes against the obligation of immediacy, but if someone does so, their fasts will still be valid. However, they will be sinful for delaying without a valid reason.

Praise be to Allah, and peace and blessings be upon our Master, the Messenger of Allah.

 

Whoever forgets an integral (Rukn) of the prayer and remembers it before reaching the equivalent point in the subsequent unit (Rak'ah), must return to it (i.e., perform it) and complete his prayer, then perform the prostration of forgetfulness (Sujud al-Sahw) at the end of his prayer. However, if he remembers it after reaching the equivalent point in the subsequent unit, the Rak'ah in which the integral was forgotten is invalidated, and the current unit takes its place; he then completes a full Rak'ah to compensate and performs the prostration of forgetfulness.

 

It is stated in Nihayat al-Muhtaj ila Sharh al-Minhaj (Vol.1/P.543): 'If he becomes certain at the end of his prayer, or after the Salam—provided the interval is not long according to custom and he has not stepped on an impurity—that he omitted a prostration from the final Rak'ah, he must perform it and repeat the Tashahhud, as his previous Tashahhud occurred before its proper place. If the omission was from a Rak'ah other than the final one, he must perform a full Rak'ah, because the deficient unit was completed by a prostration from the subsequent one, rendering the rest of that subsequent unit void.' And Allah the Exalted knows best.

Praise be to Allah, and peace and blessings be upon our Master, the Messenger of Allah.

 

It is permissible to make up (qada’) missed prayers at any time, even during the periods when prayer is generally prohibited. The prayers that are forbidden and considered invalid during these times are 'absolute voluntary prayers' (nafl mutlaq)—which have no specific cause—and voluntary prayers whose cause follows the prayer itself, such as the Sunnah of entering Ihram or the Sunnah of the Istikharah prayer. Furthermore, no prayer is considered disliked (makruh) during these prohibited times when performed within the Meccan Sanctuary (Makkah al-Mukarramah).

 

It is stated in Bushra al-Karim (Vol.1/P.181), one of the Shafi’i texts: 'It is not forbidden to perform prayers that have a cause that is not delayed (i.e., the cause is preceding), such as making up a missed prayer (fa’itah)—even if it was a voluntary one—and the funeral prayer (janazah); or a cause that is simultaneous, such as the prayer for rain (istisqa’) or the eclipse prayer (kusuf)... and the Sunnah of wudu, the greeting of the mosque (tahiyyat al-masjid), the Sunnah of circumambulation (tawaf), the Sunnah of arrival, and the prostrations of recitation (tilawah) or thankfulness (shukr). These mentioned prayers and their like are not forbidden provided that one does not specifically intend (ta'ammud) to perform them during the disliked time because it is a disliked time. If one does so intentionally, it becomes forbidden, even if it is a mandatory makeup prayer that is due immediately; because in that case, one is acting in defiance of the Sharia. This is in contrast to when one does not specifically seek out that time, even if the prayer happens to fall within it, or if one seeks it for another purpose—such as delaying a funeral prayer to that time so that a larger number of people may pray over the deceased; in such cases, it is permissible and valid... And it is forbidden to perform prayers with no cause at all, like absolute nafl, or those with a delayed cause, such as the Istikharah prayer, the prayer for Ihram, the prayer for a need (hajah), the prayer before leaving the house, or the prayer before execution; because their causes occur after the prayer itself.' And Allah the Exalted knows best."

Using an oxygen device does not affect the validity of fasting because oxygen is a gas with no physical substance.

However, if medicinal substances with physical particles are added to the oxygen, its use would break the fast, as it enters the body cavity through a natural passage.