Reference for Yevamot 201:15

ומדאיצטריך לעיני למעוטי סומים ש"מ דאפילו הדיוטות דאי סלקא דעתך סנהדרין בעינן למה לי למעוטי סומין מדתני רב יוסף נפקא דתני רב יוסף כשם שב"ד מנוקים בצדק כך ב"ד מנוקים מכל מום

— He deduces it from Before the eyes of;<span class="x" onmousemove="('comment',' Deut. XXV, 9 (E.V., In the presence of). ');">⁴⁰</span> a Master having said: 'Before the eyes of', excludes blind men. Now, since the expression 'Before the eyes of' is required to exclude blind men it follows that even laymen [are eligible]. For should it be suggested [that only members of] the Sanhedrin<span class="x" onmousemove="('comment',' I.e., professional judges. ');">⁴¹</span> are required. what need was there to exclude blind men, [an exclusion which could have been] deduced from that which R. Joseph learnt! For R. Joseph learnt: As the <i>Beth din</i><span class="x" onmousemove="('comment',' [H], lit., 'house of law' 'court', applied also to the members of the Sanhedrin or of any court engaged in legal decisions or in the administration of the law. ');">⁴²</span> must be clean<span class="x" onmousemove="('comment',' In their character, free from all possible suspicion. ');">⁴³</span> in respect of righteousness so must they be clear from all physical defects,<span class="x" onmousemove="('comment',' Heb, mum, 'blemish'. ');">⁴⁴</span>

Jastrow