Leviticus 21:2-4 New International Version Anglicized (NIVUK)

2. except for a close relative, such as his mother or father, his son or daughter, his brother,

3. or an unmarried sister who is dependent on him since she has no husband – for her he may make himself unclean.

4. He must not make himself unclean for people related to him by marriage, and so defile himself.

Leviticus 21