Reference for Yevamot 44:15

ורבנן אף על גב דכתיב אחותך איצטריך למכתב היא שלא תאמר בעלמא מזהירין מן הדין

refers to him who had intercourse with a forbidden relative and begot from her a bastard! — Now, at any rate. he is practising 'the deeds of thy people'.<span class="x" onmousemove="('comment',' Though he cannot clear his past he may turn over a new leaf. ');">¹⁴</span>

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