Sahih Bukhari | Volume 3 | Hadith Number 792

Narrated by 'Umar bin Al-Khattab
I gave a horse in Allah's Cause. The person to whom it was given, did not look after it. I intended to buy it from him, thinking that he would sell it cheap. When I asked the Prophet he said, "Don't buy it, even if he gives it to you for one Dirham, as the person who takes back what he has given in charity, is like a dog that swallows back its vomit."