Reference for Niddah 56:6

לאו משום שנאמר (במדבר ה, ג) מזכר ועד נקבה תשלחו זכר ודאי נקבה ודאית ולא טומטום ואנדרוגינוס

but no offering is incurred when the Sanctuary is hidden from him.<span class="x" onmousemove="('comment',' Sc. he well remembered when entering the Sanctuary that he was unclean but forgot that it was the Sanctuary that he was entering. ');">¹¹</span> R. Akiba stated, [Scripture says:] It being hidden from him that he is unclean,<span class="x" onmousemove="('comment',' Lev. V, 2. ');">⁹</span>

Jastrow