What is the ruling on congratulating others on the arrival of Ramadan?
Congratulating others on the arrival of Ramadan is permissible.
If someone does it to express their love for worship and the blessings of Ramadan, and congratulates their fellow Muslim, they have done something good.
The Prophet ﷺ said: "Shall I not tell you something that, if you do it, you will love one another? Spread peace (Salam) among yourselves." [Narrated by Muslim]
Giving Salam is a prayer for peace and safety.
What should one who doubts the validity of his ablution and performs it frequently do?
Whoever doubts the validity of his ablution after finishing it, his ablution is valid. This is because the default is the validity of the ablution, and because doubt after finishing an act of worship doesn`t affect its validity. And Allah the Almighty knows best.
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 eating from one`s Udhiyah?
In the Name of Allah, and may peace and blessings be upon our Master, the Messenger of Allah.
The Udhiyah (sacrificial offering) is divided into two categories: the vowed sacrifice (Al-Mandhurah) and the voluntary sacrifice (Al-Tatawwu').
First: The Vowed Sacrifice (Al-Mandhurah)
This refers to a sacrifice that has become strictly obligatory due to a formal vow (Nadr). It is completely impermissible for the person offering it, or any members of their family whom they are financially obligated to maintain, to eat any of its meat or fat. Furthermore, it is unlawful for them to personally benefit from its hide, wool, or any other part of it. If they happen to eat any portion of it, the offerer is legally obligated to give an equivalent amount of meat or its monetary value to charity. (As noted in Tuhfat al-Muhtaj by Imam Ibn Hajar al-Haytami,Vol. 9/P.364).
Second: The Voluntary Sacrifice (Al-Tatawwu’)
This is a recommended, non-obligatory sacrifice. The person offering it is fully permitted to eat from its meat, distribute portions as charity to the poor, and give pieces as gifts to those who are well-off. However, it remains a mandatory requirement to donate at least a minor portion of it to charity; this should not be less than approximately half a kilogram of raw, uncooked meat. And Allah the Almighty Knows Best.