Reference for Yevamot 63:13

ותניא כיצד אמר רבי יוסי נידון בזיקה הראשונה הבאה עליו חמותו ונעשית אשת איש נידון בחמותו אשת איש ונעשית חמותו נידון באשת איש

Does, then, R. Jose hold the view that one prohibition may be imposed upon another? Surely, it was taught: A man who committed a transgression which involves two death penalties<span class="x" onmousemove="('comment',' Intercourse, for instance, with a mother-in.law (which is punishable by burning) who was at the time a married woman (the penalty for which Is strangulation). ');">³⁸</span> is punished by the severer one. R. Jose said: He is to be dealt with In accordance with that prohibition which came into force first.<span class="x" onmousemove="('comment',' Tosef. Sanh. XII, Sanh. 81a. ');">³⁹</span> And it was taught: How is one to understand R. Jose's statement that sentence must be in accordance with the prohibition which came into force first? [If the woman was first] his mother-in-law<span class="x" onmousemove="('comment',' Having been a widow or divorcee at the time of his marriage. ');">⁴⁰</span> and then became also a married women, he is to be sentenced for [an offence against] his mother-in-law; if she was first a married woman and then became his mother-in-law, he is to be sentenced for [an offence against] a married woman!<span class="x" onmousemove="('comment',' Though the penalty in this case (strangulation) is lighter than that for an offence against a mother-in-law (burning). This proves that one prohibition may not be imposed upon another. Had it been otherwise, the severer penalty should have been inflicted though the prohibition which had caused it came into force later. ');">⁴¹</span>

Jastrow