Reference for Sanhedrin 152:12
<big><strong>גמ׳</strong></big> אמר שמואל מפני מה לא נאמרה יד בברזל שהברזל ממית בכל שהוא
Hence [incest with] his mother-in-law's mother [as a punishable offence] is arrived at [only] by [Biblical] interpretation. But R. Akiba maintained, 'he and ethe'en' means 'he and both of them', hence his mother-in-law's mother is explicitly interdicted in this verse.<span class="x" onmousemove="('comment',' Since R. Ishmael maintains that only 'one of them' is denoted by [H], it must mean his mother-in-law. Consequently, her mother is not directly referred to, and has to be deduced. But R. Akiba, translating [H] 'both of them' (which cannot possibly include his wife), regards the verse as referring to his mother-in-law and her mother; hence death by fire for the latter is explicitly taught in this verse. ');"><sup>11</sup></span>