Yoma 42B

״למשמרת למי נדה״ כתיב. אלא למעוטי השלכת עץ ארז ואזוב ושני תולעת, דלאו גופה דפרה נינהו.

this is mistaken because: “And it should be kept for the congregation of the children of Israel for a water of sprinkling” (Numbers 19:9) was written, and the use of the term “should be kept” indicates that one must maintain attention even during these stages. Rather, it is to exclude from the requirement the stage of casting the cedar wood, and the hyssop, and the strip of crimson into the fire. The requirement does not apply to this stage, as they do not pertain to the heifer itself.

איתמר: שחיטת פרה בזר, רבי אמי אמר: כשרה, ורבי יצחק נפחא אמר: פסולה. עולא אמר: כשרה, ואמרי לה: פסולה.

An amoraic dispute was stated with regard to the slaughter of the red heifer by a non-priest: R' Ami said: It is valid. And R' Yitzḥak Nappaḥa said: It is invalid. Ulla said: It is valid, but some say that he said: It is invalid.

מתיב רבי יהושע בר אבא לסיועיה לרב: אין לי אלא הזאת מימיה שאין כשרין באשה כבאיש, ואין כשרין אלא ביום.

R' Yehoshua bar Abba raised an objection to the opinion of Shmuel that the slaughter is valid, thereby providing a support for opinion of Rav, who holds that it is invalid: I have a derivation only with regard to the sprinkling of the red heifer’s waters, that they are not valid if sprinkled by a woman as opposed to when sprinkled by a man, and that the sprinkling is valid only during the day. The verse states: “And the pure one should sprinkle upon the impure on the 3rd day” (Numbers 19:19). The use of the terms “pure one,” in the masculine form, and “day,” indicate that the sprinkling is valid only if performed by a man during the day.