Polygamy

The one who boasts of receiving what he has not been given is like the one who has put on two garments of falsehood

Asmā' (may Allah be pleased with her) reported that a woman asked the Messenger of Allah (may Allah’s peace and blessings be upon him): "I have a co-wife; is it sinful for me to boast (before her) of receiving from my husband what he has not given me?" He replied: "The one who boasts of receiving what he has not been given is like the one who has put on two garments of falsehood."