This is the statute of the Torah that the Lord has commanded, saying: Speak to the children of Yisrael, and they shall take to you a red heifer, perfect, in which there is no blemish, and upon which a yoke has not been laid.
Torah Temimah: Yoma 42b — From where do we know that the slaughter, receiving of the blood, sprinkling of the blood, burning, and casting of the cedar, hyssop and crimson are valid only by day? From “Torah.” One might include even the gathering of the ashes, filling of water and sanctification; therefore it says “zos.”
English: It was taught: From where [do we know] that the slaughter of the heifer, receiving of its blood, sprinkling of its blood, its burning, and the casting of cedar wood, hyssop and crimson stuff are valid only by day? The verse says “Torah.” One might [think] I include even the gathering of its ashes, filling of water and sanctification; the verse says “zos.”
Ribui and mi’ut from the words “Torah” and “zos.”
The core sacrificial acts of the para aduma must be performed during the daytime; the later stages of gathering ashes and preparing the mei niddah are not restricted to daytime by this verse.