Once I gave a horse in Allah's Cause (in charity) but that person did not take care of it. I intended to buy it, as I thought he would sell it at a low price. So, I asked the Prophet ﷺ about it. He said, "Neither buy, nor take back your alms which you have given, even if the seller were willing to sell it for one Dirham, for he who takes back his alms is like the one who swallows his own vomit."  

سَمِعْتُ عُمَرَ ؓ يَقُولُ حَمَلْتُ عَلَى فَرَسٍ فِي سَبِيلِ اللَّهِ فَأَضَاعَهُ الَّذِي كَانَ عِنْدَهُ فَأَرَدْتُ أَنْ أَشْتَرِيَهُ وَظَنَنْتُ أَنَّهُ يَبِيعُهُ بِرُخْصٍ فَسَأَلْتُ النَّبِيَّ ﷺ فَقَالَ لاَ تَشْتَرِ وَلاَ تَعُدْ فِي صَدَقَتِكَ وَإِنْ أَعْطَاكَهُ بِدِرْهَمٍ فَإِنَّ الْعَائِدَ فِي صَدَقَتِهِ كَالْعَائِدِ فِي قَيْئِهِ  

Yahya related to me from Zayd ibn Aslam that his father said that he had heard Umar ibn al-Khattab say, "I once gave a noble horse to carry somebody in the way of Allah, and the man neglected it. I wished to buy it back from him and I thought that he would sell it cheaply. I asked the Messenger of Allah ﷺ about it and he said, 'Do not buy it, even if he gives it to you for one dirham, for someone who takes back his sadaqa is like a dog swallowing its own vomit.' "  

يَقُولُ حَمَلْتُ عَلَى فَرَسٍ عَتِيقٍ فِي سَبِيلِ اللَّهِ وَكَانَ الرَّجُلُ الَّذِي هُوَ عِنْدَهُ قَدْ أَضَاعَهُ فَأَرَدْتُ أَنْ أَشْتَرِيَهُ مِنْهُ وَظَنَنْتُ أَنَّهُ بَائِعُهُ بِرُخْصٍ فَسَأَلْتُ عَنْ ذَلِكَ رَسُولَ اللَّهِ ﷺ فَقَالَ لاَ تَشْتَرِهِ وَإِنْ أَعْطَاكَهُ بِدِرْهَمٍ وَاحِدٍ فَإِنَّ الْعَائِدَ فِي صَدَقَتِهِ كَالْكَلْبِ يَعُودُ فِي قَيْئِهِ  

"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 for Allah 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. "' (Using translation from Nasāʾī 2615)  

سَمِعْتُ عُمَرَ يَقُولُ حَمَلْتُ عَلَى فَرَسٍ فِي سَبِيلِ اللهِ فَأَضَاعَهُ الَّذِي كَانَ عِنْدَهُ فَأَرَدْتُ أَنْ أَبْتَاعَهُ مِنْهُ وَظَنَنْتُ أَنَّهُ بَائِعُهُ بِرُخْصٍ فَسَأَلْتُ عَنْ ذَلِكَ رَسُولَ اللهِ ﷺ فَقَالَ «لَا تَشْتَرِهِ وَإِنْ أَعْطَاكَهُ بِدِرْهَمٍ فَإِنَّ الْعَائِدَ فِي صَدَقَتِهِ كَالْكَلْبِ يَعُودُ فِي قَيْئِهِ»