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 ‏"‏ ‏.‏

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.