Zakah is obligatory in gold and silver, with evidence.

The Shaykh : First, regarding gold and silver: Zakah is obligatory in gold and silver. Allah the Exalted said: Hoarding gold and silver means withholding its zakah, or, if you prefer a broader expression, withholding the obligatory expenditure from it, whether that is zakah, feeding the hungry, clothing the naked, or spending on a relative whose maintenance is obligatory. The important point is that hoarding gold and silver is not burying it in the ground, but rather withholding what is due from it, such as zakah and other obligations. Now, the Prophet (peace and blessings be upon him) said: and you heard the hadith just now: So, gold and silver are zakatable wealth, whether it is growing, like the gold and silver in the hands of money changers who trade in currency exchange, or whether it is gold and silver that is not growing, like a man who has gold bars prepared for a need. A man has gold bars in his house prepared for a need; he says, "When I need it, I will sell some of it and spend on myself." Do these bars have zakah or not? They have zakah, because zakah is obligatory in gold and silver by their very nature, not by their growth.