Sahih Muslim , Book 12, Hadith 3949 (USC-MSA) ⓘ

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 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.

حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مَسْلَمَةَ بْنِ قَعْنَبٍ، حَدَّثَنَا مَالِكُ بْنُ أَنَسٍ، عَنْ زَيْدِ بْنِ أَسْلَمَ، عَنْ أَبِيهِ، أَنَّ عُمَرَ بْنَ الْخَطَّابِ، قَالَ حَمَلْتُ عَلَى فَرَسٍ عَتِيقٍ فِي سَبِيلِ اللَّهِ فَأَضَاعَهُ صَاحِبُهُ فَظَنَنْتُ أَنَّهُ بَائِعُهُ بِرُخْصٍ فَسَأَلْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم عَنْ ذَلِكَ فَقَالَ ‏ "‏ لاَ تَبْتَعْهُ وَلاَ تَعُدْ فِي صَدَقَتِكَ فَإِنَّ الْعَائِدَ فِي صَدَقَتِهِ كَالْكَلْبِ يَعُودُ فِي قَيْئِهِ ‏" ‏ ‏.‏

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."

وَحَدَّثَنِيهِ زُهَيْرُ بْنُ حَرْبٍ، حَدَّثَنَا عَبْدُ الرَّحْمَنِ، - يَعْنِي ابْنَ مَهْدِيٍّ - عَنْ مَالِكِ، بْنِ أَنَسٍ بِهَذَا الإِسْنَادِ وَزَادَ ‏ "‏ لاَ تَبْتَعْهُ وَإِنْ أَعْطَاكَهُ بِدِرْهَمٍ ‏" ‏ ‏.‏