Sahih al-Bukhari 6957, 6958

Narrated Abu Huraira:Allah's Messenger (ﷺ) said, "On the Day of Resurrection the Kanz (Treasure or wealth of which, Zakat has not been paid) of anyone of you will appear in the shape of a huge bald headed poisonous male snake and its owner will run away from it, but it will follow him and say, 'I am your Kanz.'" The Prophet (ﷺ) added, "By Allah, that snake will keep on following him until he stretches out his hand and let the snake swallow it." Allah's Messenger (ﷺ) added, "If the owner of camels does not pay their Zakat, then, on the Day of Resurrection those camels will come to him and will strike his face with their hooves." Some people said: Concerning a man who has camels, and is afraid that Zakat will be due so he sells those camels for similar camels or for sheep or cows or money one day before Zakat becomes due in order to avoid payment of their Zakat cunningly! "He has not to pay anything." The same scholar said, "If one pays Zakat of his camels one day or one year prior to the end of the year (by the end of which Zakat becomes due), his Zakat will be valid."