When does the time for Udhiyah begin?
Praise be to Allah, and peace and blessings be upon our master, the Messenger of Allah.
The time for Udhiyah (sacrificial offering) begins once the sun has risen on the day of Eid al-Adha—which is the tenth of Dhul-Hijjah—and a period of time has passed equivalent to two brief prayer units (Raka'at) and two brief sermons (Khutbah). It then continues until the sunset of the last of the days of Tashreeq, which are the eleventh, twelfth, and thirteenth of Dhul-Hijjah.
The Prophet (peace be upon him) said: "All the mountain passes of Mina are places of sacrifice, and in all the days of Tashreeq there is slaughtering." [Narrated by Al-Bayhaqi and Ibn Hibban].
The best time to slaughter is after finishing the Eid prayer, due to the saying of the Prophet (peace be upon him):
"Indeed, the first thing we begin with on this day of ours is to pray, then we return and slaughter. Whoever does that has attained our Sunnah, and whoever slaughters before [the prayer], it is only meat he has presented to his family; it is not part of the ritual sacrifice (Nusuk) in any way." [ٌReported by Bukhari & Muslim].
It is valid to sacrifice at any time, whether by night or by day; however, it is disliked (Makruh) at night. And Allah the Almighty knows best.
Is it incumbent on a father to cover the marriage costs of his son if the latter couldn`t afford them?
The son should seek the help of his relatives in order to convince his father to do the aforesaid, and the father should make sure that his son doesn`t commit fornication through helping him to get married, and Allah will reward him for doing so.
Is it valid to perform the obligatory prayer while sitting?
Praise be to Allah, and peace and blessings be upon our Master, the Messenger of Allah.
Standing (Al-Qiyam) while having the ability to do so is one of the pillars (Arkan) of the prayer; the obligatory (Faridah) prayer is not valid without it. However, whoever is unable to stand may pray sitting down. As for voluntary (Nafilah) prayers, it is permissible to pray them sitting even if one is able to stand, but the one sitting receives half the reward of the one who prays standing. And Allah the Exalted knows best.
Does the use of suppositories, enemas, or hemorrhoid creams affect the validity of fasting?
Enemas and suppositories inserted through either of the two private passages invalidate the fast. This ruling is based on the statement of Ibn Abbas (may Allah be pleased with him): "Breaking the fast occurs from what enters (the body), not from what exits." [Reported by Al-Bayhaqi in As-Sunan Al-Kubra]
His generalization regarding anything entering the body indicates that it invalidates fasting, whether it is nutritious or not, as even non-nutritious substances resemble food in form.
It is recommended to use them before Fajr or after Iftar. However, if a person must use them while fasting, they should continue refraining from food and drink for the rest of the day and make up for that day later.