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

This hadith has been narrated on the authority of Ibn Umar through another chain of transmitters

Salim reported from Ibn Umar (Allah be pleased with them) that 'Umar donated a horse in the path of Allah and then found it being sold, and he decided to buy that. He asked Allah's Apostle (ﷺ) about it, whereupon Allah's Messenger (ﷺ) said:Umar, do not get back what you gave as charity