Mishnayos Taharos Perek 2 Mishnah 4

הרביעי נאכל בנזיד הקודש (And [heave offering] in the fourth degree of ritual impurity is eaten in a pottage of Holy Things) – that is to say, that if there is in that heave offering fourth degree [of ritual impurity], as, for example, that was prepared in conditions of cleanness pertaining to Holy Things, and similarly the fifth degree [of ritual impurity] that is eaten in a pottage of Holy things, as is taught further on (in Mishnah 5 of this chapter) , this is how what he said: and if there is that Holy Thing fifth-degree [of ritual impurity] as, for example, that it was prepared in conditions of cleanness of a sin-offering of the ashes of the Red Heifer, as we stated, the clothing of those who consume Holy Things are [ritual impurity imparted] through treading (usually by someone with gonorrhea, a woman with an issue, a woman after childbirth and/or a menstruating woman) for a sin-offering is eaten in a pottage of Holy Things, it is permissible to combine in it a cooked dish of pure Holy Things.