The story of Kisa-Gotami is one of my favorites; here is the fairly well known section about going to the Buddha following the death of her son:
Then her son ran around, ran in all directions at playtime, and he died. Then the madness of grief arose in her. She said to herself, “Previously I was treated with contempt, but from the time of the birth of my son, I attained honor. They will try to throw my son away.” Because of her madness from grief, she went from door to door of the houses in the village with the dead body fastened to her hip, saying, “Give me a medicine for my son.” The people treated her with contempt, saying, “What good is medicine?” She did not understand what they said. […] The teacher saw she possessed the basis for attaining the goal. “Go, enter the town,” he said, “and bring me some white mustard seed from any house where there has never been any death.”
“Very well, sir”, she said. Pleased, she entered the town, and at the first house she said, “The Teacher has told me to bring white mustard seed as medicine for my son. If this house has never had a death, give me white mustard seed.”
“Who can count the dead people here?” they replied.
Going to the second and third houses, she thought, “What use is white mustard seed?” Through the power of the Buddha, her madness went away, and established in her normal mind, she thought, “This will be true for the whole town. The Blessed One, who is friendly and sympathetic, saw this would be so.”
She became profoundly stirred, went out and threw away her son in the cemetery. Then she said this verse:
This is not the doctrine for a village, the doctrine of a town, nor the doctrine of a family. This is the Doctrine for the whole world of men and devas: all of this is impermanent.
–
The Commentary on the Verses of the Theris, Trans. Acariya Dhammapala, 223-224.
As far as I can tell, the full recounting of this story only occurs in the commentary on the Therigatha verse of Kisa-Gotami. Is this correct, or can the story be found elsewhere as well?
