The Hot Spring
One day Guru Nanak Dev ji was traveling with his Sikhs in the Himalayas. His sikhs were hungry and there was no food. Guru Nanak sent his Companion Bhai Mardana to collect food for langar.
Many people donated rice and flour to make parsadas. The one problem was that there was no fire to cook the food.
At that point Guru Nanak used his walking stick to move a rock aside, exposing a hot spring of bubbling water.
The Sikhs were able to mix the rice and beans and shape them into parasadas, but Bhai Mardana's parasadas kept sinking into the water.
Then Bhai Mardana said I am going to donate my life in the name of God. Amazingly, at that the parsada floated to the water's surface.
Guru Nanak Dev Ji used this to make a point with his Sikhs saying, 'anyone who donates his life in the name of God, all their drowned items would, like the bread, 'float'.'
This was indeed a miracle.