It was narrated from 'Umar, meaning, from his father, his grandfather 'Umar, that :
he gave a horse in charity at the time of the Messenger of Allah (ﷺ), then he saw its owner selling it for a low price. He went to the Prophet (ﷺ) and asked him about that, and he said: "Do not buy what you gave in charity."
English reference: Vol. 3, Book 15, Hadith 2392
Arabic reference: Book 15, Hadith 2482