Narrated `Abdullah bin `Umar: `Umar bin Al-Khattab gave a horse to be ridden in Allah's Cause and then he found it being sold. He intended to purchase it. So, he consulted Allah's Apostle who said, "Don't buy it and don't take back your gift of charity."
Hadith Referenceصحيح البخاري / كتاب الجهاد والسير / 3002
Hadith Gradingمحدثین:أحاديث صحيح البخاريّ كلّها صحيحة
Narrated Aslam: I heard `Umar bin Al-Khattab saying, "I gave a horse to be ridden in Allah's Cause and the person who got it intended to sell it or neglected it. So, I wanted to buy it as I thought he would sell it cheap. I consulted the Prophet who said, "Do not buy it even if for one Dirham, because he who takes back his gift is like a dog swallowing its vomit."
Hadith Referenceصحيح البخاري / كتاب الجهاد والسير / 3003
Hadith Gradingمحدثین:أحاديث صحيح البخاريّ كلّها صحيحة