(1) باب كَرَاهَةِ شِرَاءِ الإِنْسَانِ مَا تَصَدَّقَ بِهِ مِمَّنْ تَصَدَّقَ عَلَيْهِ
Zaid b. Aslam reported on the authority of his father that 'Umar (Allah be pleased with him) donated a horse in the path of Allah. He found that it had languished in the hand of its possessor, and he was a man of meagre resources He (Hadrat 'Umar) intended to buy it. He came to Allah's Messenger (ﷺ) and made a mention of that to him, whereupon he said:
Don't buy that even if you get it for a dirham for he who gets back the charity is like a dog which swallows its vomit.
Reference: Sahih Muslim 1620 c
In-book reference: Book 24, Hadith 3
USC-MSA web (English) reference(deprecated numbering scheme): Book 12, Hadith 3950