Reference for Zevachim 113:6

וזו שאלה נשאלה לפני חכמים בכרם ביבנה בכור לכמה נאכל נענה ר"ט ואמר לשני ימים ולילה אחד

the Writ assimilated it to the breast and the thigh of a peace-offering:<span class="x" onmousemove="('comment',' Since it was the breast and the thigh of a peace-offering which belonged to the priest.');">⁸</span> as a peace-offering might be eaten during two days and one night, so may the firstling be eaten during two days and one night.

Jastrow