From Sahih Muslim (Hadith 4167):
Ibn 'Umar reported that 'Umar b. al-Khattib (Allah be pleased with him) donated a horse in the path of Allah and (later on) he found it being sold, and he decided to buy that. He asked the Messenger of Allah (ﷺ) about it. whereupon he (the Holy prophet) said:Don't buy that and do not get back what you gave in charity
Reference: Muslim 4167