Reference for Sanhedrin 101:25

אלא את אביה ברשות אביה ואת חמיה ברשות חמיה

[Ifshe committed adultery] her penalty is burning. But if she was married toone unfit for her [e.g., a bastard, etc.] she must repay the principal andthe added fifth, and her penalty is strangulation: this is the ruling ofR. Meir. But the Sages hold that in both cases she must pay the principalbut not the fifth, and her penalty is burning.

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