In Islam, there are some ceremonies and occasions which are held all around the world among Muslims. They all have religious backgrounds and are mostly referred to in the holy Quran. Muslim nations have been commemorating them in the course of history. Here we are going to have a glance at the most significant Islamic occasions based on the Lunar Calendar.
1.10th of Muharram: Martyrdom of Imam Hussain (AS)
The month of Muharram is the first month of the year in the lunar calendar. On the tenth day of this month, Hussain Ibn Ali (AS), the grandson of Prophet Muhammad (PBUH&HP), and his companions were brutally martyred, and their women and children were taken captive by the caliph of the time, Yazid ibn. Muawyah. Their story has been the source of inspiration for many new converts.
2. 20th of Safar: The Day of Arbaeen
Arbaeen is the Arabic word for forty, and it marks the 20th of Safar, the fortieth day after Imam Hussain's (AS) martyrdom on the day of Ashura, who was martyred in the event of Karbala along with his companions in the cruelest and most inhumane way possible.
According to some historical accounts , some of the members of Imam Hussain's (AS) family after being released from the bondage of Yazid's forces returned to Karbala from Sham (today's Damascus) to visit Imam Hussain's (AS) grave. Also, some believe that Imam Hussain's (AS) head, which was taken to Sham by Yazid's army was brought back to Karbala on this day and buried with his body  & .
Every year, a few days before this day, a vast number of people from all over the world, Muslims or even non-Muslims, gather in Iraq to take part in a symbolic walk, to revive the teachings of Imam Hussain (AS) and commemorate his sacrifice in the way of Allah and humanity.
3. 17th of Rabi al-Awwal: Prophet Muhammad's (PBUH&HP) Birthday
There is a disagreement concerning the exact date of Prophet Muhammad's (PBUH&HP) birthday. Some believe it occurred on the 12th of Rabi al-Avval, while others consider it to be on the 17th of Rabi al-Avval, the third month in the Islamic calendar. Prophet Muhammad (PBUH&HP) was born in Mecca. All Muslims around the world celebrate his birthday and regard it as one of the important Islamic occasions. On this day, Muslims feed the needy, pray and recite the Quran, commemorate Prophet Muhammad (PBUH&HP), and his challenges to deliver the messages of Allah to human beings.
4. 1st of Shawwal: Eid al-Fitr
The first day of the month of Shawwal, the tenth month of the Islamic calendar, is called Eid al-Fitr. After fasting for one month, during the month of Ramadan, remembering, worshipping Allah and trying to do fewer sins beside not eating and drinking from before the Call for Fajr prayer to after the Call for Magrib prayer, Muslims celebrate the first day of the month of Shawwal, for their success in submitting to Allah's command. They perform the Eid prayer first; then, they hold a feast inviting their loved ones, wear their best clothes, and visit their friends and family. The culture of feasting might be different in different Islamic communities, but one thing is for sure; no one is allowed to fast on this exceptional day. Allah also obliges Muslims to share their blessings and happiness with the needy with the money they donate to them.
5. 10th of Dhu'l-Hijjah: Eid al-Adha
Eid al-Adha is one of the most significant Islamic occasions. Some of the most important events of this Abrahamic religion happened on this day. On this Eid, similar to Eid al-Fitr, Muslims are not allowed to fast. The first is the sacrifice of Ishmael by his father, Abraham, for the sake of Allah. When Abraham and his son both surrendered, and he was ready to behead his son, Allah sent a ram and asked Abraham to kill that instead.
"So when they had both surrendered [to Allah's will], and he had laid him down on his forehead, We called out to him, 'O Abraham! You have indeed fulfilled your vision! Thus indeed do We reward the virtuous! This was indeed a manifest test. Then We ransomed him with a great sacrifice, and left for him a good name in posterity." (37: 103-108)
This day is also the last day of Hajj rituals, in which Muslims shall sacrifice an animal to feed the needy Muslims. On this day, those who attended Hajj have performed all their Hajj rituals, and with the great assistance of Allah, all their sins are wiped away, and Allah accepts their good deeds and repentance.
Many Muslims celebrate this day. They sacrifice an animal to feed the needy, even if they have not attended Hajj. If they do not have enough money to buy a sheep, they do other things and feed the destitute in different ways. This sacrifice is an expression of generosity and obedience to the commands of Allah. This Eid also reminds humankind of the characteristics, such as envy, rage, dishonesty, etc., they have to symbolically sacrifice in themselves to become the better version of themselves and be worthy of being Allah's best creation.
6. 18th of Dhu'l-Hijjah: Eid al-Ghadir
This Islamic occasion was a day in the last Hajj pilgrimage (Hajjat al-Vida'a) of Prophet Muhammad (PBUH&HP). When he was going back to Medina with all his companions and other pilgrims, he gathered everyone around a place called Ghadir and announced these words in which he appointed Imam Ali b. Abi Talib (AS) as his caliph and the Imam after himself following a direct order from Allah [i]:
"Whomsoever, I am his leader (Mawla), Ali (AS) is also his leader (Mawla). O' Allah! Love those who love him (Ali (AS)) and oppose those who oppose him" 
This is another important day in the Muslim calendar. On this day, Muslims can fast and again feed the needy, as an essential part of Islamic culture.
These are the most significant and most celebrated Islamic occasions. As one can see, feeding others and praying to Allah are the essential things a Muslim should do to celebrate a feast, which reveals the importance of caring for others in Islam that results from the devotion to Allah.
[i] Verse 67th of Surah al-Maedah known as Al-Tabligh Verse, and the third verse of the same chapter known as Al-Ikmal Verse.
 Ibn Athīr, Usd al-ghāba, vol. 3, p. 605; Kulaynī, al-Kāfī, vol. 1, p. 295; Balādhurī, Ansāb al-ashrāf, vol. 2, p. 110-111; Ibn Kathīr, al-Bidāya wa l-nihāya, vol. 7, p. 349.
 Ibn Tawus, 'Ali b. Musa, Al-Luhuf 'ala qatla l-tufuf, Uswi, Qom, 1414 AH.
 Al-Biruni, Abu Rayhan, The Remaining Signs of Past Centuries, p.331.
 Qazi al-Tabataii, Muhammad Ali, A Research on the first Arba'een of the Leader of Martyrs (Imam Hussain (AS)), vol.3, p.304.