since you did not have to exhaust your horses and camels or god granted to his messenger their property. god gives authority to his messenger over whomever he wants. god has power over all things.
وما أفاء الله على رسوله منهم فما أوجفتم عليه من خيل ولا ركاب ولكن الله يسلط رسله على من يشاء والله على كل شيء قدير