Reference for Pesachim 183:2
גר שנתגייר בע"פ ב"ש אומרים טובל ואוכל את פסחו לערב וב"ה אומרים הפורש מן הערלה כפורש מן הקבר:
IF A PROSELYTE WAS CONVERTED ON THE EVE OF PASSOVER, - BETH SHAMMAI MAINTAIN: HE PERFORMS TEBILLAH AND EATS HIS PASSOVER-OFFERING IN THE EVENING; WHILE BETH HILLEL RULE: ONE WHO SEPARATES HIMSELF FROM [THE STATE OF] UNCIRCUMCISION IS LIKE ONE WHO SEPARATED HIMSELF FROM A GRAVE.<span class="x" onmousemove="('comment',' He must be besprinkled with the water of purification on the third and seventh days after the circumcision; hence he is not yet fit in the evening.');"><sup>3</sup></span> <big><b>GEMARA: </b></big>What is the reason? - He holds: [The law of] aninuth at night is Rabbinical [only], and where the Passover offering is concerned they did not insist on their law, since it involves<span class="x" onmousemove="('comment',' Lit., 'in the place of'.');"><sup>4</sup></span>