Zayd bin Aslam (may Allah have mercy on him) said: I heard my father say that Umar bin al-Khattab (may Allah be pleased with him) said: I gave a horse (to be ridden) in the way of Allah, then I saw it being sold, so I asked the Messenger of Allah (peace and blessings be upon him): Shall I buy it? He (peace and blessings be upon him) said: "Do not buy it, and do not go back on your charity."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7631
Zayd bin Aslam narrates from his father that Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) gave a horse in the way of Allah. Then he saw some of its offspring being sold, and he wanted to buy it, so he asked the Prophet (peace and blessings be upon him) about it, and he (peace and blessings be upon him) said: "Do not buy it, and do not go back on your charity."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7632
Zayd bin Aslam narrates from his father that he said: I heard Umar bin al-Khattab (may Allah be pleased with him) say: I gave a fine horse in the way of Allah, and its owner (to whom it was given) neglected it. I wanted to buy it from him, and I thought that he would sell it to me cheaply, so I asked the Messenger of Allah (peace and blessings be upon him) about it, and he (peace and blessings be upon him) said: "Do not buy it from him even if he gives it to you for a single dirham, for the one who goes back on his charity is like the dog that goes back to its vomit."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7633
Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) said that Sayyiduna Umar (may Allah be pleased with him) gave a horse in charity in the way of Allah. Then he saw it being sold, and he intended to buy it, so he came to the Messenger of Allah (peace and blessings be upon him) and consulted him, and he (peace and blessings be upon him) said: "Do not go back on your charity." For this reason, Ibn Umar (may Allah be pleased with them both) would not buy anything that he had given in charity or by which he had sought righteousness; (if he did,) he would give it in charity.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7634