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." (FR)
English reference (FR): Vol. 3, Book 15, Hadith 2392 (FR)
Arabic reference (FR): Book 15, Hadith 2482 (FR)