The villager Yao Niu, from Xu County, was a little over ten years old when his father was killed by a fellow villager. Niu sold his clothes and bought weapons, planning to take revenge. He subsequently encountered the villager before the county gate, and stabbed him amidst the crowd. When he was captured by the clerks, the chief official felt a deep sympathy for his filial piety, allowing the case to be delayed. At the next amnesty he received a pardon. The prefectural authorities had submitted requests to the emperor on his behalf, so his treatment was unique.
Some time later, the magistrate went hunting, pursuing a deer into a wild place where there were many deep and ancient wells. His horse was about to advance into one of these when he suddenly saw an old man, who raised his staff and struck the horse. The magistrate’s mount drew up, alarmed, losing the chance to reach the deer,  but a servant drew a bow to shoot it. The old man told them: “There is a well here; I was afraid the gentleman would fall in.” The magistrate asked him: “Who are you?” The old man knelt straight-backed, and told him: “I am the father of Min Yao Niu. I am grateful for the gentleman saving Niu, and came to offer my thanks.” He then vanished from sight.
Li Fang 李昉, et al., Taiping guangji 太平廣記 (Extensive Gleanings from the Era of Great Harmony), 10 vols (Beijing: Zhonghua shuju, 1961), vii, 320.2538-39:
須縣民姚牛。年十餘。父為鄉人所殺。牛嘗賣〈賣原作殺。據明鈔本改。〉衣服。市刀戟。圖欲報讎。後在縣門前相遇。手刃之於衆中。吏擒得。官長深矜孝節。為推遷其事。會赦得免。又為州郡論救。遂得無他。令後出獵。逐鹿入草中。有古深井數處。馬將趣之。忽見一翁。舉杖擊馬。馬驚避。不得及鹿。  令奴引弓將射之。翁曰。此中有井。悲君墮耳。令曰。汝為何人。翁長跽曰。民姚牛父也。感君活牛。故來謝。因滅不見。出幽明錄