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 semi-circular structure attached to the Holy Kabah?
The semi-circular structure attached to the Holy Kabah is Hijr Al-Kabah (is a low wall originally part of the Kabah) and passing behind it is an obligation while making Tawaf because it is a part of the Holy Kabah. And Allah Knows Best.
How should I deal with the whispers of the devil with regard to ablution and purity?
Whispers in ablution are from the devil, and so you should take refuge in Allah from the devil`s evil suggestions that aim to distort the religion. Thus, once an organ is completely pure, don`t question its purity since having whispers doesn`t mean that the purity is invalid as it has already been established.
In the Sharia-compliant viewing at a prospective bride (*al-naẓrah al-sharʿiyyah*), is it permissible for the man to see the woman without a veil (*ḥijāb*)?
All praise is due to Allah, and peace and blessings be upon our master, the Messenger of Allah.
It is sunnah for the suitor to see the woman he is seeking to marry within the limits the Sharīʿah permits, namely looking at the face and the hands (palms and backs), based on the saying of the Prophet (peace and blessings be upon him): “Look at her, for it is more likely to bring about harmony between you.” Narrated by al-Tirmidhī.
The suitor may also ask one of the women to look at the woman he is seeking to marry. In that case, she is permitted to see of her what she is normally permitted to see, which is not limited to the face and hands, and she then describes these matters to the suitor. It is narrated on the authority of Anas (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) sent Umm Sulaym to look at a girl, and said: “Smell her breath, and look at her heels.” Narrated by Aḥmad in his Musnad.
It is stated in Tuḥfat al-Muḥtāj (Vol.7/p.192): “For one who cannot easily look, or does not wish to look himself, it is sunnah to send someone who is permitted to look at her, to observe her and describe her to him, even regarding what he himself is not permitted to look at. He thereby gains through the sending what he would not gain through looking. Because of the added need for this, it is excepted from the prohibition of a woman describing another woman to a man.”
The permissibility of looking is conditional upon his resolve to marry her once he is able to, his predominant assumption that his proposal will be accepted, and his assumption that the woman is free of marriage and of a waiting period (ʿiddah). Otherwise, looking is forbidden.
Accordingly, it is not permissible for the suitor to look at anything other than the face and hands. He may ask one of his maḥram women, such as his mother or sister, to see the woman unveiled, and the Sharia-compliant viewing (of a prospective bride) must take place in the presence of one of the woman’s maḥrams. And Allah Almighty knows best.