Leviticus 18:14
Thou shalt not uncover the nakedness of thy father’s brother, thou shalt not approach to his wife: she is thine aunt. Thou shalt not uncover the nakedness of thy father’s brother, thou shalt not approach to his wife: she is thine aunt.
Leviticus 18:14 stands among the Lord's direct and explicit prohibitions governing sexual conduct. It defines a boundary God Himself established to guard and preserve the purity of His people. Any sexual familiarity that uncovers nakedness in the manner it forbids is sin. Such conduct is never a liberty to be indulged or treated as permissible.