Reference for Menachot 159:2
אלא אולד תודה נדבה בין לפני כפרה בין לאחר כפרה אין טעונין לחם מותר דתודה היא אלא אולד תודה חובה לפני כפרה טעון לחם לאחר כפרה אין טעון לחם
Shall I then say [it refers] to the case of the young of a freewill thank-offering? But surely whether [it is offered] before the atonement or after the atonement it certainly does not require the bread-offering, for it is the surplus of the thank-offering?<span class="x" onmousemove="('comment',' Any accretion to the original thank-offering is accounted as surplus and, like the surplus of money that was assigned for the purchase of a thank-offering, does not require the bread-offering.');"><sup>3</sup></span> - I must say [it refers] to the case of the young of an obligatory thank-offering; thus if [the young is offered] before the atonement it requires the bread-offering, but if after the atonement it does not require the bread-offering.