It was narrated from Zaid bin Aslam that his father said: “I heard ‘Umar say: ‘I gave a horse to someone to ride in the cause of Allah, the Mighty and Sublime, and the one who kept it neglected it. I wanted to buy it back from him, and I thought that he would sell it at a cheap price. I asked the Messenger of Allah صلی اللہ علیہ وآلہ وسلم about that and he said: Do not buy it, even if he gives it to you for a Dirham. The one who takes back his charity is like the dog that goes back to its Own vomit.’” (Sahih)