Reference for Pesachim 41:15
ומוכרו לנכרי: פשיטא לאפוקי מהאי תנא דתניא ב"ש אומרים לא ימכור אדם חמצו לנכרי אא"כ יודע בו שיכלה קודם פסח וב"ה אומרים כל שעה שמותר לאכול מותר למכור
For what purpose does he state, CATTLE and for what purpose does he state BEASTS? They are necessary: for if he stated CATTLE, [I might say.] that is because if they leave over it is fit for them;<span class="x" onmousemove="('comment',' Later; they leave it on the ground and eat it later.');"><sup>12</sup></span> but [as for] BEASTS, which if they leave over hide it,<span class="x" onmousemove="('comment',' With the result that the leaven may remain in his possession during Passover.');"><sup>13</sup></span> I would say [that it is] not [so]. While if he stated BEASTS, [ might say]. that is because if they leave over they at least hide it;<span class="x" onmousemove="('comment',' So that it is not seen.');"><sup>14</sup></span> but as for cattle, sometimes they leave over and he [the owner] may not think about it,<span class="x" onmousemove="('comment',' To annul it before Passover, thinking it was already eaten.');"><sup>15</sup></span> and so transgress<span class="x" onmousemove="('comment',' Lit., stands'.');"><sup>16</sup></span> 'it shall not be seen and 'it shall not found' on its account, [and therefore] I might say [that it is] not [so]: thus they [both] are necessary. What i the purpose of BIRDS? - Because he states CATTLE and BEASTS, he also states BIRDS. AND HE MAY SELL IT TO A GENTILE. That is obvious?<span class="x" onmousemove="('comment',' Surely this is no worse than any other benefit.');"><sup>17</sup></span> It is to reject [the view of] this Tanna. For was taught: Beth Shammai maintain: A man must not sell his leaven to a Gentile, unless he knows thereof that it will be consumed before Passover; but Beth Hillel say: As long as he [the Jew] may eat it, he may sell it.