Mustadrak al-Hakim — Hadith 1468

Sayyiduna Ubayy bin Ka'b (may Allah be pleased with him) states: The Prophet (peace and blessings be upon him) sent me to collect zakah. I passed by a man, and he gathered his wealth before me, and nothing was due from him except a one-year-old she-camel (bint makhad). I said: Give a one-year-old she-camel; that is your zakah. He said: That gives neither milk nor can it be ridden; take this best, young and fat she-camel of mine instead. I said: I cannot take what I have not been commanded to take. The Messenger of Allah (peace and blessings be upon him) is near you; if you wish, go to him and offer him what you have offered me. If he (peace and blessings be upon him) accepts it, I will accept it, and if he (peace and blessings be upon him) returns it, I will return it. He said: I will do so. So he set out with me, bringing the she-camel he had offered me, until we reached the Messenger of Allah (peace and blessings be upon him). He said: O Prophet of Allah! Your envoy came to me to take the zakah of my wealth. By Allah! Never before has the Messenger of Allah (peace and blessings be upon him) or any envoy of his come for (the zakah of) my wealth. I gathered my wealth for him, and he said that a one-year-old she-camel is due from me, but that gives neither milk nor can it be ridden. I offered him a large she-camel to take, but he refused. O Messenger of Allah! This is that she-camel, which I have brought to you, so accept it. The Messenger of Allah (peace and blessings be upon him) said: "What was due from you was that (one-year-old she-camel), but if you wish to give this better she-camel willingly, Allah will reward you for it and we will accept it." He said: O Messenger of Allah! Here is that she-camel; I have brought it to you, so accept it. So the Messenger of Allah (peace and blessings be upon him) ordered that it be taken and prayed for blessing in his wealth.
This hadith is sahih (authentic) on the condition of Imam Muslim, but the two Shaykhs did not record it.