Reference for Chullin 59:6
ובמועד לשמו פטור שלא לשמו חייב
R'Idi B'Abin raised this objection: [We have learnt: If a man slaughtered the paschal lamb whilst having leaven in his possession] during the festival<span class="x" onmousemove="('comment',' The proper time for slaughtering the paschal lamb was on the eve of the Passover festival and it is enjoined in Ex. XXIII, 18, that at the time of slaughtering the paschal lamb - and indeed at the time of slaughtering any sacrifice during the Passover festival (v. Pes. 63a) there must be no leaven in one's possession. In our case the circumstances were these: A lamb was originally set apart for the paschal offering but was lost, and another was offered as a sacrifice in its place. Subsequently, the original lamb was found and is now being offered on the festival as a sacrifice.');"><sup>4</sup></span>