Who is the one deemed "able" (al-qādir), for whom the uḍḥiyah (sacrificial offering) is sunnah?
All praise is due to Allah, and peace and blessings be upon our master, the Messenger of Allah ﷺ.
The one who is deemed "able" (al-qādir) [to perform the uḍḥiyah, i.e., the sacrifice] is someone who possesses wealth sufficient to acquire the sacrificial animal, over and above what is needed to cover his own living expenses and the living expenses of his wife and children — or of anyone else whose financial support (nafaqah) is legally obligatory upon him — for the day of ‘Eid and the three days of Tashrīq [that follow it], since this is the designated time period for the sacrifice. And Allah, the Exalted, knows best.
Who is the one required to slaughter the 'aqīqah?
All praise is due to Allah, and may peace and blessings be upon our Master, the Messenger of Allah.
It is Sunnah for the 'aqīqah to be slaughtered by the guardian of the newborn — the one upon whom the child's financial maintenance is obligatory — provided he is financially capable of doing so. 'Alī ibn Abī Ṭālib, may Allah be pleased with him, reported: "The Messenger of Allah ﷺ performed the 'aqīqah for al-Ḥasan with one sheep." — Narrated by al-Tirmidhī. And Allah Almighty 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.
A man led the people in prayer as imam, and at the end of the prayer he performed a prostration of forgetfulness (*sujūd al-sahw*) because he had omitted a short *sūrah* after al-Fātiḥah. What is the ruling on his prayer and that of those praying behind him?
All praise is due to Allah, and peace and blessings be upon our master, the Messenger of Allah.
According to the Shāfiʿī school, it is sunnah to recite a sūrah after al-Fātiḥah in the prayer. One who omits it has a valid prayer, and no prostration of forgetfulness (sujūd al-sahw) is prescribed for omitting it. If someone performs sujūd al-sahw for its omission while knowing the ruling and remembering it, his prayer is invalidated. But one who is ignorant of the ruling, or who did so out of forgetfulness, his prayer is not invalidated, because this is among the matters that are obscure to people, and ignorance of it is not restricted to those who recently entered Islam.
Shaykh al-Islām al-Shams al-Ramlī said in Nihāyat al-Muḥtāj ilā Sharḥ al-Minhāj (Vol.2/p.70): “The remaining sunnahs are not compensated for by prostration, such as the remembrances (adhkār) of bowing and prostration, that is, the opening supplication (duʿāʾ al-iftitāḥ) and the sūrah, in accordance with the base rule, because they are not of the same nature as what has been reported [as compensable]. If one prostrates for any of them deliberately, his prayer is invalidated, unless he is excused due to ignorance. As for the objection raised that the ignorant person does not know that sujūd al-sahw is prescribed, and whoever knows it knows its place, this is refuted by denying such a necessary connection, for the ignorant person may hear only that sujūd al-sahw is prescribed before the salām, and so assume that it applies to every sunnah and is not restricted to its prescribed place.”
This is among the matters that are obscure, in which the mukallaf is excused for ignorance, as stated by al-Shabrāmallisī in his Ḥāshiyah ʿalā Nihāyat al-Muḥtāj (Vol.2/p.70).
However, if the imam prostrates, and the follower (maʾmūm) presumes that his imam’s prostration is for a reason for which one does not prostrate, it is not permissible to follow him in it, so long as the follower knows the ruling.
Accordingly, the prayer of one who did not recite a sūrah after al-Fātiḥah is valid, and sujūd al-sahw is not prescribed for it. Whoever prostrates out of ignorance or forgetfulness, his prayer is valid, because this is among the issues hidden from the general public. But whoever prostrates while knowing the ruling and remembering it, his prayer is invalidated. And Allah Almighty knows best.