When is the prayer considered *adāʾ* (performed within its time): upon rising from the bowing (*rukūʿ*), or after rising from the prostration (*sujūd*)?
All praise is due to Allah, and peace and blessings be upon our master, the Messenger of Allah.
Whoever catches one complete rakʿah within the prayer's time has caught the prayer as an on-time (adāʾ) prayer. The rakʿah is complete when the worshipper raises his head from the second prostration (sajdah), even if he has not yet reached the degree of standing in which the recitation is valid.
It is stated in Nihāyat al-Muḥtāj (Vol.1/p.378): "What is meant by the rakʿah is the completion of all of it, with its two prostrations." End quote.
And in Ḥāshiyat al-Shabrāmallisī: "(His saying: 'a rakʿah') means that he raises his head from the second prostration, even if he has not reached the degree in which the recitation is valid." And Allah Almighty knows best.
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Note on terminology: Adāʾ refers to performing the prayer within its prescribed time, as opposed to qaḍāʾ (making it up after its time has ended).
What is the ruling on someone who combines two prayers as an early combination (jam‘ taqdīm), and then arrives at his place of residence during the time of the second prayer — is he obligated to repeat it?
All praise is due to Allah, and peace and blessings be upon our master, the Messenger of Allah ﷺ.
Whoever combines Ẓuhr and ‘Aṣr while traveling — that is, before he has reached the built-up boundaries of his hometown [upon returning] — his combination (jam‘) of the two prayers remains valid, even if he arrives at his place of residence before the time for the second prayer has actually begun. This is because the combination was already validly completed with its proper conditions fulfilled, and he is not obligated to repeat the second prayer [upon arrival].
A traveler is permitted to make use of the concessions of shortening (qaṣr) and combining (jam‘) prayers once the distance of travel reaches (81 km) or more, provided that his journey is a permissible one, and that he begins shortening and combining only after actually setting out on the journey and passing beyond the built-up limits of the city in which he resides. And Allah, the Exalted, knows best.
What is the ruling on praying seated due to severe obesity, given that I experience hardship in performing the prayer — especially when rising from the ground after sujūd to perform the next rak‘ah?
All praise is due to Allah, and peace and blessings be upon our master, the Messenger of Allah ﷺ.
Standing, when one is able to do so, is a pillar of the prayer. However, whoever would experience severe, intolerable hardship, or fears harm to himself or to a limb due to obesity, or finds that standing causes him to lose his khushū‘ (humble focus and concentration) in prayer, then there is no objection to his praying seated on a chair or on the ground, performing rukū‘ (bowing) and sujūd (prostration) through gesture — provided that the gesture for sujūd is made lower than that for rukū‘. Whoever is able, at any point, to properly perform any one of these pillars, is obligated to perform it in full; for omitting it is a concession that applies only in cases of genuine inability. The Prophet ﷺ said: "When I command you to do something, do of it whatever you are able." (Related by al-Bukhārī). As the scholars of fiqh have established: what remains possible is not waived on account of what is difficult.
The criterion for determining genuine inability, as chosen by Imam al-Ḥaramayn al-Juwaynī (raḥimahullāh), is that the worshipper experiences hardship that causes him to lose his khushū‘.
As for voluntary (nafl) prayer, there is no objection to performing it while seated, even if one is able to stand. However, rukū‘ and sujūd must still be performed [in their proper physical form] by anyone who is able to do so. And Allah, the Exalted, knows best.
What is the ruling on ablution without istinja' after sleep?
The sleep of one whose buttocks are not firmly seated on the ground invalidates ablution. Whoever wakes up and wants to pray must perform ablution only. Istinja' is not a condition for the validity of ablution, because it is for removing impurity from the private part. If there is no impurity on the private part, then istinja' is neither obligatory nor recommended. And Allah the Almighty knows best.