Reference for Shevuot 28:14
לעולם דידע בטומאת שרץ וכגון דנגע בכעדשה ולא ידע כעדשה אי מטמא אי לא מטמא מאי כיון דידע דמטמא שרץ בעולם ידיעה היא או דלמא כיון דכעדשה לא ידע אי מטמא אי לא מטמא העלמה היא תיקו
Surely, this is taught in school!<span class="x" onmousemove="('comment',' Lit., 'go, read it in school'. All children know that the carcass of a reptile contaminates (Lev. XI, 29, 30) . His temporary forgetfulness of this law is, therefore, immaterial. He is reckoned as having knowledge at the beginning, and later, when eating holy food (having forgotten that he is unclean) , there is unawareness in the middle; ultimately, when the knowledge at the end comes to him, he brings a sliding scale sacrifice. Had ignorance of the law been counted as unawareness, there would have been, in this case, no knowledge at the beginning, and he would not be liable for a sacrifice.');"><sup>21</sup></span> - Well then, he did know that a reptile is unclean, but, for example, he touched [a portion of a reptile] the size of a lentil; and he did not know whether the size of a lentil contaminates or not: What [is th ruling]?