Reference for Kiddushin 24:9

ועל חתנא דדייר בי חמוה דדייר אין חליף לא והא ההוא חתנא דחליף אבבא דבי חמוה ונגדיה רב ששת ההוא מידם הות דיימא חמתיה מיניה

Only him who dwelt, but not him who merely passed by [his mother-in-law's house]? But a certain son-in-law passed by his mother-in-law's door, for which R'Shesheth chastised him? - There his mother-in-law was [already] under suspicion through him. The Nehardeans maintained: For all these Rab inflicted no punishment, excepting for betrothing [a woman] by intercourse without shiddukin - others state, even with shiddukin, on account of licentiousness.<span class="x" onmousemove="('comment',' Tosaf.: this view is relied upon nowadays, in that sons-in-law live with their mothers-in-law.');">²¹</span>

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