Reference for Pesachim 219:2
לא יעשה צרכיו תרי אמאי נמלך הוא אמר אביי הכי קאמר לא יאכל תרי וישתה תרי ולא יעשה צרכיו אפילו פעם אחת דילמא חליש ומיתרע
Has he not [newly] decided?<span class="x" onmousemove="('comment',' The second is occasioned by a new desire, and does not combine with, the first.');"><sup>2</sup></span> -Said Abaye, This is what he [the Tanna] means: He must not eat in pairs and drink in pairs and he must not perform his needs even once [after eating or drinking in pairs], lest he be weakened<span class="x" onmousemove="('comment',' Through intimacy.');"><sup>3</sup></span> and be affected.<span class="x" onmousemove="('comment',' Since eating or drinking in pairs has already made him more susceptible to hurt than he would otherwise have been.');"><sup>4</sup></span>