Reference for Yoma 91:10

גופא אמר רב הונא תמיד תחילתו דוחה סופו אינו דוחה

[To turn to] the main text: The continual offering suspends the Sabbath only at its beginnings not at its end. What does it not suspend? - R'Hisda says: It suspends the Sabbath, but not the law of levitical impurity.

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