How is the niṣāb (minimum threshold) of gold calculated when one owns gold of multiple different karats?
All praise is due to Allah, and peace and blessings be upon our master, the Messenger of Allah ﷺ.
Zakāh is obligatory on cash and on gold designated for saving or for trade, provided the total reaches the niṣāb (minimum threshold liable for Zakah), and a full ḥawl (lunar year) has elapsed over it. The niṣāb is (85) grams of 24-karat gold; for 21-karat gold, the niṣāb equals (97) grams; and for 18-karat gold, it equals (113) grams.
If one owns gold of multiple different karats, the person paying zakāh should calculate the monetary value of all the gold he owns, combining these values together to determine whether the total reaches the niṣāb. He then pays zakāh on this combined monetary value, once the total reaches the niṣāb. The relied-upon position is to calculate the zakāh based on the buying price [i.e., the price the gold merchant would pay the owner to purchase the gold from him] on the day the zakāh obligation is due. And Allah, the Exalted, knows best.
What is the ruling on congregational prayer performed outside the mosque, and is it a condition that it be performed in a mosque in order to attain the full reward?
All praise is due to Allah, and peace and blessings be upon our master, the Messenger of Allah ﷺ.
It is not a condition for attaining the reward of congregational prayer that it be performed in a mosque; however, a Muslim should still be keen to perform his prayers in the mosque, so as not to miss out on immense reward. This is due to the virtue of the mosque and of spending time there (i‘tikāf), the typically larger number of worshippers present, and the additional reward gained through walking to and from the mosque. On the authority of Abū Hurayrah (raḍiyallāhu ‘anh), the Messenger of Allah ﷺ said: "Whoever purifies himself in his house, then walks to one of the houses of Allah to fulfill one of the obligations Allah has prescribed, one of his steps will erase a sin, and the other will raise him a degree [in status]." (Related by Muslim)
Whoever misses congregational prayer at the mosque should still strive to pray in congregation at his workplace, or together with the members of his household. And Allah, the Exalted, knows best.
What is the ruling on istinja' after urination, and is it done with water and soap or with water only?
Istinja' from urine and stool is obligatory. It is permissible to perform istinja' with water alone, or with toilet paper alone. The best way is with toilet paper then water. If one wishes to suffice with one of them, then water is better. And Allah the Almighty knows best.
I vowed to give a specific charity if a certain matter came to pass — what is the ruling on giving that charity before the matter is realised?
All praise is due to Allah, and peace and blessings be upon our master the Messenger of Allah ﷺ.
Fulfilling a vow (nadhr) is obligatory, in accordance with the word of Allah the Almighty: "And let them fulfil their vows." [Al-Ḥajj/ 29] And the saying of our master the Messenger of Allah ﷺ: "Whoever vows to obey Allah, let him obey Him; and whoever vows to disobey Him, let him not disobey Him." (Reported by al-Bukhārī.)
The Shāfiʿī scholars distinguished between a financial vow (nadhr mālī) and a bodily vow (nadhr badanī). They permitted the fulfilment of a financial vow to be brought forward — before the stipulated condition is met — but did not permit the same for a bodily vow, which may only be fulfilled after the condition has actually been realised.
Shaykh al-Islām Imām Zakariyyā al-Anṣārī, may Allah have mercy upon him, states: "It is permissible to bring forward the fulfilment of a financial vow before the condition stipulated in it is met — such as saying: 'If I am healed, I vow to free a slave' or 'to give such-and-such in charity' — just as it is permissible to pay zakāh in advance. This is unlike a bodily vow, such as fasting." [Asnā al-Maṭālib, vol. 4/P.246]
Imām al-Bājūrī, may Allah have mercy upon him, states: "Like expiation other than fasting, a financial vow — such as saying: 'If Allah heals my sick one, I vow to free a slave for the sake of Allah,' or 'If Allah heals my sick one, I vow to free a slave on the Friday following the recovery' — it is permissible to bring it forward before the recovery in the first case, and before the Friday following the recovery in the second case." [Ḥāshiyat al-Bājūrī ʿalā Sharḥ Ibn Qāsim, Vol.2/P.596] And Allah the Almighty knows best.