On the prohibition against describing a woman's beauty to a man when there is no legitimate need for that, for instance, like seeking marriage with her, etc.

Riyad as-Salihin (The Meadows of the Righteous)

by Imam Nawawi

331. Chapter: On the prohibition against describing a woman's beauty to a man when there is no legitimate need for that, for instance, like seeking marriage with her, etc.

1742. Ibn Mas'ud reported that the Messenger of Allah, may Allah bless him and grant him peace, said, "A woman should not embrace another woman and then describe her to her husband so as to give him an exact picture of her." [Agreed upon]