June 16.
On this day, every year since 1606, Sikh's have commemorated the martyrdom of the Fifth Guru, Guru Arjan Dev Ji.
During the "leadership" of Guru Arjan Dev Ji, people in India then known as Hindustan [Muslims, Hindus] were all converting to Sikhism under Guruji's teachings. At this time, the Mughal Clergy was greatly upset over the growing conversion to Sikhism and the Emperor of India of the time, Akbar did nothing to stop it, angering the Mughal clergy further. In 1605, after Akbar died the Clergy through Jahangir sought to make the whole of Hindustan an Islamic state as Jahangir was a fundamentalist Muslim unlike his father Akbar.
Making use of Guru Arjan Dev Ji's enemies, the Clergy was enable to throw baseless allegations at Guruji. Some of which were that the Granth Sahib [Holy Book] defamed Hindus and Muslims. In late May 1606, Guru Arjan Dev Ji was arrested and brought to Lahore where he suffered full 6 days [One day-->arrested] of torture.
Guruji was forbade to sleep, eat or drink.
O Waheguru! Your actions seem so sweet to me
Har naam padarath naanak maangi
Nanak begs for the treasure of the Naam, the name of the Lord

Day 4
Guru Arjan Dev forbade his Disciplines to help him any way possible. "Such is the Will of my God, submit to the Divine Will, move not, stand calm against ill woes."
As soon as he took a dip, his body was no where to be found. "Hail to the Master. Thou art Wonderful- Martyr, the greatest. Thou art the greatest!"
Guru Arjan Dev ji was First Sikh Guru who complied the hymns of various saints and spiritual guru's into one collection called Guru Granth Sahib.He wrote maximum number of hymns for Guru Granth Sahib.
[This paragraph credit: sami01]
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