‘Udhiya’ is an Arabic word meaning ‘Sacrifice’;  ‘Qurbani’ is a Persian word derived from the Arabic word ‘Qurban’ which means an act performed to seek Allah’s pleasure.  There is nothing dearer to Allah SWT than sacrificing an animal in the name of Allah on the day of Eid-ul-Adha. When a person slaughters an animal on this day, he/she is forgiven at the fall of the first drop of blood and the rewards from this act will be brought forward on the Day of Judgment for this person.  The aim of sacrifice, like all other fundamentals of Islam, is to earn piety and self righteousness.   Allah SWT says, “Their meat will not reach Allah, nor will their blood, but what reaches Him is piety from you” [22:37].  – In a different Ayat it is mentioned, “So turn in prayer towards your Lord and sacrifice (animals) [108.2]. 

Origin of Qurbani: This act of Qurbani is to commemorate the unparalleled sacrifice offered by the Prophet Ibrahim AS. When he, in pursuance to a command of Allah SWT conveyed to him in a dream, prepared himself to slaughter his beloved son Ismail, but Allah SWT after testing his submission, sent down a ram and saved his son from the logical fate of slaughter. It is from that time onwards that the sacrifice of an animal became obligatory on believers. 

Virtues of Qurbani: Of all of the physical and spiritual worships the greatest is Salah (Namaz) and among the worships concerning wealth, animal sacrifice holds a distinguished place in Islam.  Prophet PBUH said, "The son of Adam does not perform any action on the day of sacrifice (Eid-ul-Adha ) which is more pleasing to Allah than shedding blood (of slaughtered animals). He will come on the day of resurrection with its hair, horns and hooves, and the blood certainly will fall in a place near Allah before it falls on the ground. So, make yourselves purified there with” [Tirmizi]. -  When Prophet PBUH was asked about the rewards of Qurbani, He PBUH replied, “the person performing Qurbani will be rewarded for every hair on the body of the animal or for every fibre of wool in the case of sheep” [Ahmed].

Days of Qurbani:  The days of sacrifice are the 10th, 11th, and 12th of Zhul Hijah. The actual time commences from after the Eid prayer and lasts just until before sunset on the 12th of Zul Hijah. Although it is permissible to make sacrifice during the night, it is not advisable. The best day for the sacrifice is on the day of Eid.   Prophet PBUH said, "He who has performed our Salah and slaughtered the animal like us (after the Eid Salah), he has indeed correctly discharged his Qurbani. However, he who has slaughtered his animals before the Salah, there is no Qurbani for him" [Bukhari].  This Hadith emphasizes the importance of sacrifice after the Eid prayer.

On whom it is Wajib:  Qurbani is Wajib on every Muslim who is of sound mind, has reached the age of puberty, Muqeem (not a traveler) and possesses the amount of 612.36 grams of silver (or 19.68 ounces of gold ) or wealth equivalent to that value which is in excess of one's basic needs.  It is not necessary that this amount be in one's possession for a complete lunar year. It's possession during the three days of Qurbani (10th, 11th, 12th of Zul Hijah) will make Qurbani obligatory. 

No Alternative for Udhiya:  Some people think that instead of offering a ritual slaughter (Qurbani), they can give its amount to the poor as charity. This is not correct. There are different forms of worship obligatory on Muslims. Each one has its own importance and none of them can stand for the other. As an example, It is not permissible for a Muslim to perform Salat instead of fasting in Ramadan, nor is it permissible to give charity instead of observing the obligatory Salat. Similarly, Qurbani is an independent form of worship and cannot be discharged by spending money in charity. However, if an individual, out of ignorance or negligence, could not offer it on the three prescribed days (10th, 11th, 12th of Zul-Hijah) then, he can give the price of a ritual slaughter as Sadaqah to those entitled to receive Zakat.