Reference for Sanhedrin 116:19
מגביה עבדו שבת סימן: אמר ריש לקיש המגביה ידו על חבירו אע"פ שלא הכהו נקרא רשע שנאמר (שמות ב, יג) ויאמר לרשע למה תכה רעך למה הכית לא נאמר אלא למה תכה אף על פי שלא הכהו נקרא רשע
But Raba said thus: A heathen <font>who violates his neighbour's wife unnaturally is free from punishment</font> — Why so? — <font>[Scripture saith:] <i>To</i> his <i>wife</i>, but not to his neighbour's; <i>and he shall cleave</i>, which excludes unnatural intercourse</font>.<span class="x" onmousemove="('comment',' By taking the two in conjunction, the latter as illustrating the former, we learn that the guilt of violating the injunction 'to his wife but not to his neighbour's wife' is incurred only for natural, but not unnatural intercourse. ');"><sup>20</sup></span>