So she went to the Buddha, laid the body of her child at his feet, and told him her story. The Buddha listened with infinite compassion. Then he said gently, “There is only one way to heal your affliction. Go down to the city and bring me back a mustard seed from any house in which there has never been a death.”

Krisha Gotami felt elated and set off at once for the city. She stopped at the first house she saw and said: “I have been told by the Buddha to fetch a mustard seed from a house that has never known death.”
“Many people have died in this house,” she was told. She went on to the next house. “There have been countless deaths in our family,” they said. And so to a third and a fourth house, until she had been all around the city and realized the Buddha’s condition could not be fulfilled.

She took the body of her child to the charnel ground and said goodbye to him for the last time, then returned to the Buddha.
“Did you bring the mustard seed?” he asked.
“No,” she said. “I am beginning to understand the lesson you are trying to teach me. Grief made me blind and I thought that only I had suffered at the hands of death.”
“Why have you come back?” asked the Buddha.
“To ask you to teach me the truth,” she replied, “of what death is, what might be behind and beyond death, and what in me, if anything, will not die.”

The Buddha began to teach her: “If you want to know the truth of life and death, you must reflect continually on this: There is only one law in the universe that never changes – that all things change, and all things are impermanent. Because pain has now made you ready to learn and your heart is opening to truth, I will show it to you.”

Krisha Gotami knelt at his feet, and followed the Buddha for the rest of her life."

Pg 28-29,  The Tibetan Book of Living and Dying
Sogyal Rimpoche

Rigpa Fellowship, 1993