Sayyiduna Ubayy bin Ka'b (may Allah be pleased with him) narrates that the Prophet (peace and blessings be upon him) sent me as a zakah collector. I passed by a man, and he gathered his wealth together, and I saw that a bint makhad was due from him. So I said to him: "Pay a bint makhad, for that is your zakah." He said: That is an animal that has neither milk nor is fit for riding; but this is a fine young she-camel, take it. I said: "I will not take what I have not been commanded to take. The Messenger of Allah (peace and blessings be upon him) is staying nearby; if you wish to give this, go to him (peace and blessings be upon him) and present to him what you have presented to me. If he (peace and blessings be upon him) accepts it, I will accept it too, and if he (peace and blessings be upon him) rejects it, I will return it too." He said: I will do so. He narrates: So he set off with me, and that she-camel was with him, until we came to the Messenger of Allah (peace and blessings be upon him). He said: O Prophet of Allah! Your collector came to me to take the zakah of my wealth. By Allah! Never before has any envoy of yours come to my wealth. I gathered my wealth before him, and he holds that the zakah on my wealth is only one bint makhad, and that is an animal that has neither milk nor is fit for riding. So I offered him a fine young she-camel, but he refused to take it, and this is it; I have brought it to you (peace and blessings be upon him). O Messenger of Allah! Accept it. The Messenger of Allah (peace and blessings be upon him) said to him: "What is due from you is that; but if you voluntarily give something better than it, Allah Almighty will reward you for it, and we will accept it from you." He said: O Messenger of Allah! This is it; I have brought it to you, so accept it. So he (peace and blessings be upon him) ordered that it be received and prayed for blessing in his wealth.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7279