In the book of Leviticus, God instructs the Israelites on the offerings they are to make. And he repeats eighteen times* that the offering shall be "without blemish", that it should have "no blemish" (Lev 22:21).

In Leviticus 22:20, God says: "You shall not offer anything that has a blemish, for it will not be acceptable for you."

*these passages are:
1:3,10; 3:1,6; 4:3,23,28,32; 5:15,18; 6:6; 9:1,3; 14:10 (twice); 22:19; 23:12,18