Warning against withholding zakah, with a mention of the evidence for this from the Book and the Sunnah.

The Shaykh : And it is known to every reader of the Qur'an that Allah has threatened those who are stingy with zakah with a severe and terrible threat. Among this is His saying, the Exalted: And how is this encircling? The Prophet (peace and blessings be upon him), the most knowledgeable of creation regarding the meanings of the Book of Allah, explained it by saying that the wealth is represented to him on the Day of Resurrection as a bald, venomous serpent. Do you know what a "shuja'" is? The "shuja'" is the large male of the cobra, and "aqra'" means bald-headed, having no fuzz on its head, and this is due to the abundance of its venom, may Allah protect us from it, to the extent that its hair has been torn off. It has two "zabibahs," meaning two glands filled with venom. It takes hold of his "lahazmatayn," meaning the "lahazmatayn" of the owner of the wealth who was stingy with it, meaning it bites him and says: "I am your wealth, I am your treasure." And it only takes hold of the "lahazmatayn" because the owner of the wealth in this world eats it with his cheeks and boasts of it to people with his words, so he fills his cheeks with boasting. So the punishment is that this wealth takes hold of his "lahazmatayn" and says: "I am your wealth, I am your treasure." And consider how his regret will be when this wealth that torments him on that day says: "I am your wealth, I am your treasure." This wealth, which he used to protect in this world and withhold what Allah obligated him to pay from it, will be on the Day of Resurrection a rebuke for him and a blame for him. And Allah, Mighty and Majestic, said: On the Day it is heated in the Fire of Hell, and their foreheads, their flanks, and their backs are branded with it. This is what you hoarded for yourselves, so taste what you used to hoard. And those who hoard gold and silver are those who do not pay its zakah, even if they placed it on the tops of mountains. As for those who pay its zakah, it is not a hoard for them, even if they buried it in the seventh earth. And how is this branding? Listen to its explanation from the most knowledgeable of people regarding the Book of Allah, Muhammad (peace and blessings be upon him), who said: Thus they are branded with it. They are not branded with it for a day, a month, or a year, but on a Day whose measure is fifty thousand years. And one of us in this world cannot endure a spark from the fire of this world, even though the fire of this world is far less than the fire of the Hereafter. The fire of the Hereafter is preferred over the fire of this world by sixty-nine parts, to which is added one part of the fire of this world, so its heat is seventy times that of the fire of this world. I ask Allah to protect me and you from it.