It is narrated from Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) that Sayyiduna Umar bin Khattab (may Allah be pleased with him) had provided a mount for jihad, but later saw it being sold and intended to buy it. He asked the Messenger of Allah (peace and blessings be upon him) about this, and he (peace and blessings be upon him) said: "Do not buy it, and do not take back your charity."
Hadith Referenceالسنن المأثورة / باب ما جاء في صدقة الفطر / 371
Hadith Takhrijصحیح بخاری، الجہاد، باب الجعائل والحملان فی السبیل، رقم : 2971، صحیح مسلم، الہبات، باب کراہۃ شراء الانسان .... الخ، رقم : 1621۔ سنن ابن ماجہ رقم الحدیث : 1827 ، وقال :الالبانی حسن۔