Is the marriage contract considered valid if concluded at home by the marriage official (Ma`zon)?
Yes, it is valid as long as it is registered at the court.
What is the ruling on the prayer of one who said "Subḥāna Rabbiya al-ʿAẓīm" in prostration (*sujūd*) and forgot to correct it?
All praise is due to Allah, and peace and blessings be upon our master, the Messenger of Allah.
Saying “Subḥāna Rabbiya al-ʿAẓīm” in bowing (rukūʿ) and “Subḥāna Rabbiya al-Aʿlā” in prostration (sujūd) is one of the hayʾāt (non-essential sunnahs) of the prayer. Whoever omits it, whether deliberately or by forgetfulness, or replaces it with another remembrance (dhikr), his prayer is valid and he does not perform sujūd al-sahw. Shaykh al-Islām Imam al-Nawawī (may Allah have mercy on him) said: “Our school holds that one does not prostrate for omitting the audible or silent recitation, the tasbīḥ, and the rest of the hayʾāt.” [al-Majmūʿ, Vol.4/p.127]
If he performs sujūd al-sahw for something that does not call for it, his prayer is invalidated, because he introduced a prostration of forgetfulness without a cause, and he must repeat the prayer. The exception is one who did so out of forgetfulness or ignorance, whether because he recently entered Islam or because he lives far from scholars; he is excused and his prayer is not invalidated.
It is stated in Mughni al-Muḥtāj (Vol.1/p.417): “It is stated in al-Anwār: If he does something that does not call for sujūd al-sahw, thinking that it does, and then prostrates, his prayer is not invalidated if he is ignorant because he recently entered Islam or because he is far from scholars.”
Since this issue is hidden from the laity, as it is among the subtleties of knowledge, and the laity are excused for ignorance of whatever is of such a nature, and their act of obedience is not invalidated because of it, it may be said that the prayer of one who has not acquired knowledge of the issue is not invalidated. As for after knowing it, the prayer is invalidated.
Whoever realizes while still in the prayer that his prostration was out of place, it is sunnah for him to perform sujūd al-sahw. And Allah Almighty knows best.
What is the ruling on praying alone (munfaridan) in a row, and what should I do if I enter the mosque together with another person, and there is only a single gap in the first row with no second row present — should I fill that gap in the first row, or should I stand together with him in a new second row?
All praise is due to Allah, and peace and blessings be upon our master, the Messenger of Allah ﷺ.
If a person enters [the congregation] and finds no space available in the row, it is recommended for him — after making his opening takbīr for the prayer — to gently pull someone from the row in front of him to pray alongside him, provided he senses that this person would be agreeable to it. If that person does not agree, then he prays alone, and there is no dislike attached to his doing so in that case.
If he ends up praying alone [behind the row], it is sunnah for him to stand directly behind the imam. Then, if someone else arrives, that person stands to his right; and whoever comes after them stands to his left — and so on — such that the imam remains centered in the middle of the row. This is done so that everyone attains the reward of congregational prayer.
As for the case where two people enter the prayer together, and there is a gap in the row wide enough for only one person, then the two of them should pray together in a new row [of their own], and whoever arrives after them should fill that original gap. This is because if only one of the two fills the gap, the other would end up praying alone [which is to be avoided when it can easily be prevented].
Al-Khaṭīb ash-Shirbīnī (raḥimahullāh) said in Mughnī al-Muḥtāj (Vol.1/P.494): "If he does not find space, then it is recommended for him, while still standing, to gently pull a single person from the row toward himself after making his opening takbīr — out of caution, so as to avoid the position held by some scholars that a person's prayer standing alone behind the row is not valid.
Az-Zarkashī and others said: this should only be done if it seems he would agree to it; otherwise, he should not pull anyone — indeed, doing so becomes impermissible, out of fear of causing discord (fitnah). It is recommended for the person being pulled to cooperate and agree, so that he may attain the reward of assisting in righteousness and piety (al-birr wat-taqwā). However, he should not pull one of two people [praying together] from the row, since this would cause one of them to end up praying alone. This is why the 'pulling' described here takes place only after the opening takbīr [i.e., once the person doing the pulling has already validly begun his own prayer]."
Accordingly: it is sunnah for you to pray alongside the person praying alone, and then, if someone else arrives afterward, you may go and fill the gap in the original row. And Allah, the Exalted, knows best.
What can a menstruating woman do on Laylat al-Qadr?
If a menstruating woman engages in remembrance of Allah (dhikr), supplication (du‘a), and sincere devotion, she has indeed observed Laylat al-Qadr. She may also listen to the Quran from audio sources such as the radio or television.