وعن عمر بن الخطاب رضي الله عنه
قال: حملت على فرس في سبيل الله فأضاعه الذي كان عنده، فأردت أن أشتريه، وظننت أنه يبيعه برخص، فسألت النبي صلى الله عليه وسلم فقال: «لا تشتره ولا تعد في صدقتك وإن أعطاكه بدرهم، فإن العائد في صدقته كالعائد في قيئه»
I donated a horse in the way of Allah. Its new possessor did not treat it properly. I made my mind to buy it because I thought that he would sell it at a cheap price (now that it became weak and emaciated). I asked the Prophet (sallallahu alayhi wa sallam) about it, whereupon he said, “Do not buy it and do not get back your charity, for one who gets back the charity is like a dog that eats its own vomit.”
Riyad as-Salihin 1613, Book 18, The Book of the Prohibited actions, Hadith 103. 1 min read