[qs:108:2]
Zayd lbn Arqam (RA) relates that the Companions (ra) asked, "O Rasulullah! (Saw) What is Qurbani?" He replied, "It is the sunnah of your father lbraheem (as)." They asked again, "What benefit do we get from it?" He answered, "A reward for every hair (of the sacrificed animal)." "And (what reward is there for animals with) wool, 0 Rasoolullah (Saw)?" they asked. "A reward", he said, "for every fibre of the wool.", (Ibne Majah)
Aishah (ra) narrated that the Prophet Muhammad (Saw) said, "There is nothing dearer to Allah during the days of Qurbani than the sacrificing of animals. The sacrificed animal shall come on the Day of Judgement with its horns, hair, and hooves (to be weighed). The sacrifice is accepted by Allah before the blood reaches the ground. Therefore sacrifice with an open and happy heart" (Tirmidhi, p. 275, Vol.1).
Qurbani is wajib upon every Muslim who is of sound mind, mature (who has reached the age of puberty), muqeem (i.e. he is not a Shar'ee traveler) and possesses 612.36grams of silver or wealth equivalent to that value which is in excess of one's aslee (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 will make Qurbani obligatory.
The Time of Qurbani (Udhiyyah)
Qurbani is only valid during three days of Dhul Hijjah, 10th, 11th, and 12th. Qurbani cannot be performed on any other day of the year
Although Qurbani is permissible on each of the three days, the first day (10th of Dhul Hijjah) is the most preferable and desired day
Qurbani is not allowed before Eid Salah
Qurbani can be performed during night time. However, it is preferable to perform it during the daytime.
Distribution of the Meat
If an animal is sacrificed on behalf of more than one person, like a cow or camel, its meat should be distributed equally among its owners by weighing the meat strictly and not at random or by mere guess. Even if all the partners agree on its distribution without weighing, it is still not permissible according to Shariah
However, if the actual weighing is not practicable due to some reason, and all the partners agree to distribute the meat without weighing, distribution by guess can be done with the condition that each share necessarily contains either a leg of the animal or some quantity of its liver
Although the person offering a Qurbani can keep all its meat for his own use, yet, it is preferable to distribute one-third among the poor, another one-third among his relatives and then, keep the rest for his personal consumption
All parts of the sacrificed animal can be used for personal benefit, but none can be sold, nor can be given to the butcher as a part of his wages. If somebody has sold the meat of the animal or its skin, he must give the accrued price as Sadaqah to a poor man who can receive Zakah
No Alternative for Qurbani
Some people think that instead of offering a ritual slaughter (Qurbani) they should give its amount to some poor people as charity. This attitude is totally wrong. Actually, there are different forms of worship obligatory on Muslims. Each one of them has its own importance and none of them can stand for the other. It is not permissible for a Muslim to perform Salah instead of fasting in Ramadhan, nor is it permissible for him to give some charity instead of observing the obligatory Salah. Similarly, Qurbani is an independent form of worship and this obligation 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 and 12th of Dhu’l Hijjah) then, in that case only, he can give the price of a ritual slaughter (Udhiyyah) as Sadaqah to those entitled to receive Zakah. But during the days of Udhiyyah, no Sadaqa can discharge the obligation.
More info here