(119) باب الْجَعَائِلِ وَالْحُمْلاَنِ فِي السَّبِيلِ
Narrated `Abdullah bin `Umar:
`Umar gave a horse to be used in Allah's Cause, but later on he found it being sold. So, he intended to buy it and asked Allah's Messenger (ﷺ) who said, "Don't buy it and don't take back your gift of charity."
Reference: Sahih al-Bukhari 2971
In-book reference: Book 56, Hadith 180
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 4, Book 52, Hadith 215