Prohibition of describing the Beauty of a Non-Mahram Lady
It is prohibited to see a non-Mahram woman as because of this a man’s heart starts leaning towards the non-Mahram woman. In this, there is a very strong possibility of trouble. In the same way, when a woman speaks about the beauty of a non-Mahram woman in front of her husband and describes the beauty of that lady, the man starts imagining and visualizing her. Here too there is possibility of trouble as with the visualizing through eyes.
That’s why the Holy Prophet (Sallallahu alaihi wa sallam) has prohibited women from meeting such a woman who mention their beauty before her own husband. As there is a Hadith is Sunan Abu Dawood:
Translation: It has been narrated on the authority of Abdullah bin Mas’ud (May Almighty Allah be well pleased with him) that he heard that the Holy Prophet (Sallallahu alaihi wa sallam) say: No woman should meet another woman with the intention of describing (the other lady’s) beauty before her own husband in such a (detailed) manner as if he himself is seeing her. (Sunan Abu Dawood, Babu Ma Yu'maru Bihee Min Gahddhil Basar, Hadith No. 2152)