the first: that it is to be distributed to the same recipients as zakat;
the second: that it is to be spent as fayʾ (state revenue from non-military conquest).
Nothing in the Sunnah explicitly supports either view over the other. For that reason I concluded in Ahkam al-Rikaz that its disbursement is left to the discretion of the Muslim ruler, who may place it wherever the state’s welfare requires. This is also the opinion chosen by Abu ʿUbayd in al-Amwal.
Apparently this is likewise the Hanbali position, for they say regarding rikaz: “It is spent in the same unrestricted manner as fayʾ, for every public interest.”

Under the heading “Newly Acquired Wealth” he writes: “Whoever already possesses trade goods or livestock that reach the niṣāb, and during the year the goods yield profit or the livestock reproduce, must pay zakat on all of it—both the original capital and the gain—and there is no disagreement about this.”

I say: He probably means there is no disagreement among the four schools; otherwise Ibn Ḥazm dissented, saying: “Every gain is subject to zakat only after its own year has elapsed, not the year of what he already owns of the same kind, even if their years become mixed.”

See his detailed discussion in al-Muḥallā, 6/83–86. This view is closer to the plain sense of the Prophet’s statement, peace and blessings be upon him: “No zakat is due on wealth until a year has passed over it.” Yet because it can be burdensome in certain cases, the more practical course is to attach the profit to the principal and pay zakat on both together. For further discussion consult Abu ʿUbayd’s al-Amwal.