He gave a horse as a contribution in the cause of Allah, then later saw it being sold and wanted to buy it. The Prophet ﷺ said to him, "Do not take back what you gave in charity."
أخبرنا هارون بن إسحق قال حدثنا عبد الرزاق عن معمر عن الزهري عن سالم بن عبد الله عن أبيه
أنه حمل على فرس في سبيل الله فرآها تباع فأراد شراءها فقال له النبي ﷺ لا تعرض في صدقتك
Muslim narrated it in "The Book of Gifts," chapter "The dislike of a person buying back what he gave in charity," etc., hadith no. 1621, from the hadith of Abdul-Razzaq. Bukhari also narrated it (see the following hadith, from the hadith of Zuhri with this wording), and it is in Al-Kubra, hadith no. 2398, and in Musaf Abdul-Razzaq, 9/117, hadith no. 16572. Tirmidhi also narrated it in "The Book of Zakat," chapter "What has been mentioned regarding the dislike of taking back charity," hadith no. 668, from Harun with this wording, and he said, hasan sahih.