AR'BAINA Ashura marks the 40th Day commemoration after the martyrdom of Imam Hussain (a.s) alongside his 72 companion among whom were household of the holy prophet (saws) on the plain of Kar'bala on the day of Ashura : www.nairaland.com/811368/ashura-commemorating-martyrdom-imam-hussain

FIRST AR'BAINA Ashura!

"In the first Arba'een gathering in the year 62 AH, Jabir ibn Abd-Allah, a companion of the Prophet, was one of the people who performed a pilgrimage to the burial site of Husayn. Due to his infirmity and probable blindness, he was accompanied by Atiyya
bin Saad. His visit coincided with that of the
surviving female members of the Prophet's family and Husayn's son and heir Imam Zain-ul-Abideen, who had all been held captive in Damascus by Yazid I, the Umayyad Caliph. Imam Zain-ul-Abideen had
been too ill to participate in the Battle of Karbala. He later devoted his life to Azadari and spreading the message of Imam Hussain's supreme sacrifice."

"Arba'een is consistently among the largest peaceful gatherings in history. In 2008, approximately nine million religious observers converged on Karbala to commemorate Arba’een. However, in 2009, the number of people visiting Karbala on Arba'een significantly increased. According to the official website of BBC News and Press TV (Iran), over ten million people had reached the city of Karbala one or two days before Arba'een. The number of pilgrims was expected to rise to 18 million during the next two days, Arbaeen reached over 18 million in 2013."

~(Wikipedia)

en.m.wikipedia.org/wiki/Arba'een

"Peace Be Upon Hussain...the Day he was born...the Day he was martyred...the Day he will be Resurrected"

ﺍﻟﻠﻬﻢ ﺍﻟﻌﻦ ﺍﻭﻝ ﻇﺎﻟﻢ ﻇﻠﻢ ﺣﻖ ﻣﺤﻤﺪ ﻭﺁﻝ ﻣﺤﻤﺪ ﻭﺁﺧﺮ ﺗﺎﺑﻊ ﻟﻪ
ﻋﻠﻰ ﺫﻟﻚ!ﺍﻟﻠﻬﻢ ﺍﻟﻌﻦ ﺍﻟﻌﺼﺎﺑﺔ ﺍﻟﺘﻲ ﺟﺎﻫﺪﺕ ﺍﻟﺤﺴﻴﻦ ﻭﺷﺎﻳﻌﺖ
ﻭﺑﺎﻳﻌﺖ ﻭﺗﺎﺑﻌﺖ ﻋﻠﻰ ﻗﺘﻠﻪ!ﺍﻟﻠﻬﻢ ﺍﻟﻌﻨﻬﻢ ﺟﻤﻴﻌﺎ!

Ar'ba'een is the 40 days after the commemoration of the martyrdom of Imam Hussain (as) on Ashura.it marks the return of the captives of the Ahlul-Bayt (as) return and also the visitation of Jabir Ibn Abdullah al-Ansari (RA) to the grave of Imam Hussain (as).Jabir (ra) was a companion of Prophet Muhammad (sa).yearly,faithfuls walk in a symbolic gesture to Karbala.it seems in northern Nigeria,faithfuls who cannot make it to Karbala to march to the tomb of Imam Hussain (as),march to Zaria where the spiritual leader of the islamic movement is based-i.e. Sheikh Ibrahim Zakzaky.

you can read more about Ar'baeen and its significance in Islam:
https://www.nairaland.com/811368/ashura-commemorating-martyrdom-imam-hussain/3#9936199

https://www.nairaland.com/1563396/arbain-40days-after-ashura-largest

Arbaeen also has been the largest peaceful human gathering on earth for successive years.since the removal of Saddam and the Shia Muslim faithfuls (the majority in Iraq is Shia) regained freedom in Iraq,faithfuls have annually commemorated both Ashura and Ar'baeen.and for successive years,over an estimated 10-20 million faithfuls have converged on Karbala to mark Ar'baeen.

"According to the official website of BBC News and Press TV (Iran), over ten million people had reached the city of Karbala one or two days before Arba'een. The number of pilgrims was expected to rise to 18 million during the next two days, Arbaeen reached over 18 million in 2013."

http://en.m.wikipedia.org/wiki/Arba'een

Yaa Hussain...