Umar b. Khattab (Allah be pleased with him) reported:I donated a pedigree horse in the path of Allah. Its possessor made it languish. I thought that he would sell it at a cheap price. I asked Allah's Messenger (ﷺ) about it, whereupon he said: Don't buy it and do not get back your charity, for one who gets back the charity is like a dog who swallows its vomit
This hadith has been narrated on the authority of Malik b. Anas with the same chain of transmitters but with this addition:" Don't buy that even if he gives you for one dirham
Zaid b. Aslam reported on the authority of his father that 'Umar (Allah be pleased with him) donated a horse in the path of Allah. He found that it had languished in the hand of its possessor, and he was a man of meagre resources He (Hadrat 'Umar) intended to buy it. He came to Allah's Messenger (ﷺ) and made a mention of that to him, whereupon he said:Don't buy that even if you get it for a dirham for he who gets back the charity is like a dog which swallows its vomit