Once I gave a horse (for riding) in Allah's Cause. Later I saw it being sold. I asked Messenger of Allah ﷺ (whether I could buy it). He said, "Don't buy it, for you should not get back what you have given in charity." (Using translation from Bukhārī 2636)   

عُمَرُ بْنُ الْخَطَّابِ ؓ حَمَلْتُ عَلَى فَرَسٍ فِي سَبِيلِ اللهِ فَرَأَيْتُهُ يُبَاعُ فَسَأَلْتُ رَسُولَ اللهِ ﷺ أَشْتَرِيهِ فَقَالَ لَا تَشْتَرِهِ وَلَا تَعُدْ فِي صَدَقَتِكَ  

[Machine] Umair ibn al-Khattab rode on a horse in the way of Allah and saw something from its produce being sold. He wanted to buy it, so he asked the Prophet ﷺ. The Prophet ﷺ said, "Do not buy it, nor include it in your charity."  

حَمَلَ عُمَرُ بْنُ الْخَطَّابِ ؓ عَلَى فَرَسٍ فِي سَبِيلِ اللهِ فَرَأَى شَيْئًا مِنْ نِتَاجِهِ يُبَاعُ فَأَرَادَ شِرَاءَهُ فَسَأَلَ النَّبِيَّ ﷺ فَقَالَ لَا تَشْتَرِهِ وَلَا تَعُدْ فِي صَدَقَتِكَ  

[Machine] "Regarding this, the Messenger of Allah ﷺ said, 'Do not buy it, even if he gives it to you for one dirham, for the return on his charity is like a dog that returns to its vomit.'"  

عَنْ ذَلِكَ رَسُولَ اللهِ ﷺ فَقَالَ لَا تَشْتَرِهِ وَإِنْ أَعْطَاكَ بِدِرْهَمٍ وَاحِدٍ فَإِنَّ الْعَائِدَ فِي صَدَقَتِهِ كَالْكَلْبِ يَعُودُ فِي قَيْئِهِ  

[Machine] That Umar gave a horse in the cause of Allah as charity, but then he found it being sold. So, he wanted to buy it back. He then went to the Messenger of Allah ﷺ and sought his guidance in this matter. The Messenger of Allah ﷺ told him not to count it as part of his charity. From that point on, Ibn Umar used to refrain from buying anything that he had given as charity or used for a good cause, except that he would consider it as an act of charity.  

أَنَّ عُمَرَ تَصَدَّقَ بِفَرَسٍ فِي سَبِيلِ اللهِ فَوَجَدَهُ يُبَاعُ بَعْدَ ذَلِكَ فَأَرَادَ أَنْ يَشْتَرِيَهُ ثُمَّ أَتَى رَسُولَ اللهِ ﷺ فَاسْتَأْمَرَهُ فِي ذَلِكَ فَقَالَ لَهُ رَسُولُ اللهِ ﷺ لَا تَعُدْ فِي صَدَقَتِكَ فَبِذَلِكَ كَانَ ابْنُ عُمَرَ يَتْرُكُ أَنْ يَبْتَاعَ شَيْئًا تَصَدَّقَ بِهِ أَوْ بَرَّ بِهِ إِلَّا جَعَلَهُ صَدَقَةً