Whoever makes a pilgrimage to the holy shrine of Imam Hussein (pbuh)
near the Euphrates river,
is like the one who visits God at his throne

imam Raze PBUH ( thawab al-A'mal p147)

Among the five signs of a believer is :
Pilgrimage of Imam Hussain (PBUH) on Arbaeen [the 40th day following Ashura],

Imam Hasan al-Askari (Wasa’il ush-Shi’a)

Arbaeen is the period which marks the return and release of the family of Prophet Muhammad
who were held captive by the forces of the tyrant Caliph Yazid Ibn Muawiyah, following
the brutal martyrdom of Hussain Ibn Ali - the grandson of Muhammad on the land of
Karbala. The battle which took place on the 10th day of Muharram, known as the day of
Ashura also witnessed the assassination of 72 of Hussain's closest companions and family
members who included his own children, and brother, Abbas Ibn Ali.