Sahih Muslim Book - 24, Hadith - 4163

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 فِى سَبِيلِ اللَّهِ فَأَضَاعَهُ صَاحِبُهُ فَظَنَنْتُ أَنَّهُ بَائِعُهُ بِرُخْصٍ فَسَأَلْتُ رَسُولَ اللَّهِ -صلى الله عليه وسلم- عَنْ ذَلِكَ فَقَالَ « لاَ تَبْتَعْهُ وَلاَ تَعُدْ فِى صَدَقَتِكَ فَإِنَّ الْعَائِدَ فِى صَدَقَتِهِ كَالْكَلْبِ يَعُودُ فِى قَيْئِهِ ».

It was narrated from Zaid bin Aslam, from his father, that 'Umar bin Al-Khattab said: "I donated a fine horse (to be ridden in Jihad) in the cause of Allah, and its owner neglected it. I thought that he would sell it for a cheap price, and I asked the Messenger of Allah (s.a.w) about that. He said: 'Do not buy it, and do not take back your charity, for the one who takes back his charity is like the dog that returns to its vomit."