Explanation:

 During the year 1663, when Guru Har Krishan Sahib were in Delhi, a swear epidemic of cholera and smallpox broke out. The seven year old Guru attended to and served the suffering people with complete devotion. By his grace, the lake at Bangla Sahib provided a cure for thousands of peoples. In the process of serving the diseased, the Guru was himself seized by high fever and an attack of smallpox, eventually passing away on 30th March 1664, aged just eight years. The Guru wished that nobody mourn his death, rather instructing the Sikhs to sing hyms from the Gurbani. The Tenth Nanak, Guru Gobind Singh Sahib, later paid tribute to Guru Har Krishan Sahib by stating “Let us think of the holy Har Krishan, whose sight dispels all sorrow”, which forms a part of the daily Sikh prayer Ardas.