Deuteronomy 18:8

חלק כחלק יאכלו THEY SHALL ENJOY LIKE PORTIONS — This teaches that they (the priests who come to Jerusalem on the festivals as pilgrims but are not in charge) participate in the hides (of the burnt offerings due on the festivals) and the flesh of the he goats brought as sin-offerings on account of the festivals. One might think that they participate also in sacrifices which are offered not on account of the festivals, as, for instance, the continual burnt offerings, the additional offerings due on account of Sabbath (on which a festival happens to fall) and vow- and free-will offerings! Scripture, however, states: לבד ממכריו על האבות [THEY SHALL ENJOY LIKE PORTIONS] EXCEPT THE SALE OF THE FATHERS — i.e. except those things which their ancestors sold to each other in the days of David and Samuel when the system of shifts was established and they made, as it were, an agreement of sale, saying, “Take thou the ordinary priestly perquisites during thy week and I shall take them during my week (Sifrei Devarim 169:3; Sukkah 56a).

חֵ֥לֶק כְּחֵ֖לֶק יֹאכֵ֑לוּ לְבַ֥ד מִמְכָּרָ֖יו עַל־הָאָבֽוֹת׃ {ס}        

They shall have like portions to eat, besides that which comes of the sale of his patrimony.