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 should a person, who doubts the validity of his Wudu, or over performs it, do?
One who doubts the validity of his/her Wudu while performing it should redo it until he/she is certain of having attained purity. But, if doubt was after having performed Wudu, then he/she should not pay attention to that as doubt after the end of an act of worship does not count. This is of course in case doubt was within the reasonable limits since once it goes beyond that, it becomes a whispering of the Shaytaan (devil) which he/she should ignore as the Wudu is valid.
Is it permissible for an elderly person, a pregnant woman, or someone with a chronic illness to pay fidyah before Ramadan begins?
It is not permissible for an elderly person, a pregnant woman, or someone with a chronic illness to pay fidyah before Ramadan begins.
Additionally, it is not allowed to pay fidyah for more than one day in advance, because fidyah is a substitute for fasting, and fasting is not yet obligatory at that time.
However, it is permissible to pay fidyah for a single day in advance, by analogy with paying zakat up to one year in advance.
Is it a condition that a woman should untie her locks while making Ghusl (ritual bath)?
Ghusl from Janabah (ritual impurity), or menstruation obligates that water reaches the roots of the hair in order for the Ghusl to be valid, but if it doesn`t, then hair locks must be untied for water to reach them, and for Ghusl to become valid.