Musar for Shabbat 193:18

אי הכי ג' נמי ותו הא דתנן המשלשל דפנות מלמעלה למטה אם הן גבוהין מן הארץ שלשה טפחים פסולה הא פחות מג' כשרה

If so, the same should apply to three also? Moreover, when we learnt: If one lets down walls from above to below,<span class="x" onmousemove="('comment',' The reference is to the walls of a sukkah (booth, v. Lev, XXIII. 42). He takes a wall, e.g.. of boards, lowers it, but not right down to the ground, and fastens it to something on top. ');">³¹</span> if they are three handbreadths high above the ground, it [the <i>sukkah</i>] is unfit,<span class="x" onmousemove="('comment',' As the walls are incomplete. ');">³²</span>

Shemirat HaLashon