Leviticus 21:1

And the LORD said to Moses, "Speak to the priests, the sons of Aaron, and say to them: "None shall defile himself for the dead among his people,

Surrounding context

21:1 And the LORD said to Moses, "Speak to the priests, the sons of Aaron, and say to them: "None shall defile himself for the dead among his people,

21:2 except for his relatives who are nearest to him: his mother, his father, his son, his daughter, and his brother;