Imamat 19:31

19:31 Do not turn to the spirits of the dead and do not seek familiar spirits ¹  to become unclean by them. I am the Lord your God.

Imamat 18:16

18:16 You must not have sexual intercourse with your brother’s wife; she is your brother’s nakedness. ² 

¹ sn The prohibition here concerns those who would seek special knowledge through the spirits of the dead, whether the dead in general or dead relatives in particular (i.e., familiar spirits; see J. E. Hartley, Leviticus [WBC], 321, and B. A. Levine, Leviticus [JPSTC], 134). Cf. Lev 20:6 below.

² sn Regarding the last clause, see the notes on vv. 7 and 10 above.