John Gill Commentary Ezekiel 4:15

"Then he said unto me, See, I have given thee cow`s dung for man`s dung, and thou shalt prepare thy bread thereon." — Ezekiel 4:15 (ASV)

Then he said to me
The Lord listened to the prophet's prayer and argument, and makes some abatement and alteration in the charge he gave him: lo, I have given you cow's dung for man's dung :
that is, allowed him to make use of the one instead of the other, in baking his mingled bread: you shall prepare your bread with it ;
having gathered cow's dung, and dried it, he was to burn it, and bake his bread with it, which is meant by preparing it. In some parts of our nation, where fuel is scarce, cow's dung is made use of; it is gathered and plastered on the walls of houses, and, dried in clots, is taken and burnt.