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  

Yahya related to me from Malik from Nafi from Abdullah ibn Umar that Umar ibn al-Khattab gave a horse to carry some one in the way of Allah, and then he wished to buy it back. So he asked the Messenger of Allah ﷺ about it, and he said, "Do not buy or take back your sadaqa."  

أَنَّ عُمَرَ بْنَ الْخَطَّابِ حَمَلَ عَلَى فَرَسٍ فِي سَبِيلِ اللَّهِ فَأَرَادَ أَنْ يَبْتَاعَهُ فَسَأَلَ عَنْ ذَلِكَ رَسُولَ اللَّهِ ﷺ فَقَالَ لاَ تَبْتَعْهُ وَلاَ تَعُدْ فِي صَدَقَتِكَ  

Yahya said that Malik was asked about whether a man who gave some sadaqa, and then found it being offered back to him for sale by some one other than the man to whom he had given it, could buy it or not, and he said, "I prefer that he leaves it."  

قالَ يَحْيى: سُئِلَ مالِكٌ عَنْ رَجُلٍ تَصَدَّقَ بِصَدَقَةٍ، فَوَجَدَها مَعَ غَيْرِ الَّذِي تَصَدَّقَ بِها عَلَيْهِ، تُباعُ، أيَشْتَرِيها؟ فَقالَ: تَرْكُها أحَبُّ إلَيَّ.