Eid-Ul-Adha ( the Feast of Sacrifice or Day of Sacrifice) is observed after the Hajj. Eid-Ul-Adha is observed after the conclusion of the Hajj. The first day of this celebration is held on the 10th day of Dhul Hijjah

The celebration of Eid-Ul-Adha is in commemoration of the command given by Allah (SWT) to Prophet Abraham (AS) to sacrifice his first born son Ismaeel(AS) to Him. The fulfillment of this noble command of Allah (SWT) by Prophet Abraham (AS) signifies his faith in Allah.

قُلۡ إِنَّ صَلَاتِى وَنُسُكِى وَمَحۡيَاىَ وَمَمَاتِى لِلَّهِ رَبِّ ٱلۡعَـٰلَمِينَ (١٦٢)
لَا شَرِيكَ لَهُ ۥ‌ۖ وَبِذَٲلِكَ أُمِرۡتُ وَأَنَا۟ أَوَّلُ ٱلۡمُسۡلِمِينَ (١٦٣)  
سُوۡرَةُ الاٴنعَام

"Say: Truly, my prayer and my service of sacrifice, and my living and my dying are for God (alone), the Sustainer of all the worlds, in Whose Divinity none has a share. Thus I have been bidden-and I am foremost among those who surrender themselves unto Him" (Surah  Al-An'am . 162-163).

The celebration of Eid Ul Adha, reminds every muslim of his own submission to Allah (SWT), and his willingness to sacrifice anything to Allah (SWT's) wishes.

The Prophet (SAW) delivering a Khutba said, "The first thing to be done on this day (first day of Eid ul Adha) is to pray; and after returning from the prayer we slaughter our sacrifices (in the name of Allah) and whoever does so, he acted according to our Sunna (traditions)." (Sahih Bukhari).