And Kisa Gotami had an only son, and he died. In her grief she carried the dead child to all her neighbors, asking them for medicine, and the people said: “She has lost her senses. The boy is dead.” At length Kisa Gotami met a man who replied to her request: “I cannot give thee medicine for thy child, but I know a physician who can.” The girl said: “Pray tell me, sir; who is it?” And the man replied: “Go to Sakyamuni, the Buddha.”
Kisa Gotami repaired to the Buddha and cried: “Lord and Master, give me the medicine that will cure my boy.” The Buddha answered: “I want a handful of mustard-seed.” And when the girl in her joy promised to procure it, the Buddha added: “The mustard-seed must be taken from a house where no one has lost a child, husband, parent, or friend.” Poor Kisa Gotami now went from house to house, and the people pitied her and said: “Here is mustard-seed; take it!” But when she asked: “Did a son or daughter, a father or mother, die in your family?” They answered her: “Alas the living are few, but the dead are many. Do not remind us of our deepest grief.” And there was no house but some beloved one had died in it.
Kisa Gotami became weary and hopeless, and sat down at the wayside, watching the lights of the city, as they flickered up and were extinguished again. At last the darkness of the night reigned everywhere. And she considered the fate of men, that their lives flicker up and are extinguished. And she thought to herself: “How selfish am I in my grief! Death is common to all; yet in this valley of desolation there is a path that leads him to undying who has surrendered all selfishness.”
(taken from http://www.sacred-texts.com/bud/btg/btg85.htm)