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."
A woman tells the Messenger of Allah (may Allah’s peace and blessings be upon him) that her husband is married to a second wife and that she (the one asking the question) would like to say to the other wife: "My husband gave me such-and-such," while she is lying. She would only say this to anger her co-wife and make her jealous. She asked the Messenger if she would be sinful for doing this. The Messenger (may Allah's peace and blessings be upon him) told her that the one who embellishes himself by claiming to have what he does not have is someone who is lying and claiming falsehood.