Because sometimes, watching the sun go down is proof enough.
Gurudwara Bangla Sahib is the most prominent Sikh gurdwara, or Sikh house of worship, in Delhi, known for its association with the eighth Sikh Guru, Guru Har Krishan Ji. Gurdwara Bangla Sahib was originally a bungalow belonging to Raja Jai Singh, an Indian ruler in the seventeenth century, and was known as Jaisinghpura Palace. The eighth Sikh Guru, Guru Har Krishan resided here during his stay in Delhi in 1664.
During that time, there was a smallpox and cholera epidemic, and Guru Har Krishan helped the suffering by giving aid and fresh water from the well at this house. Soon he too contracted the illness and eventually died on March 30, 1664.
Guru Har Krishan Ji was only five years old when he succeeded his father - Guru Har Rai Ji - as Guru. When Guru Har Rai Ji was asked who among his two sons Ram Rai and Har Krishan would be the next guru. Guru Ji asked the person to go with a needle and insert the needle in the leg of the bed where these two sat and recited baani.
The sevadaar did the same and he was surprised to see that the needle went inside the bed when Guru Har Krishan Ji was doing paath but not when Baba Raam Rai was doing it. The sevadaar obviously perplexed went to Guru Har Rai Ji to ask the meaning. Guru Ji explained that although both of them were reciting the same baani, needle going inside the bed was symbolic of softness in the heart of Har Krishan Ji. Since the child guru was to take up so many diseases on his own self, softness was of prime importance. Thus next Guru came to be Guru Har Krishan Ji at the age of 5 years. Its the first time in the history when the light of the Guru had entered a small child.