What is the ruling on women exchanging private nightwear among themselves?

The general rule regarding a woman borrowing clothes is permissibility. Imam Bukhari dedicated a chapter to this, and Ibn Hajar narrated Aisha's evidence for the permissibility of borrowing clothes for a bride and others.

However, concerning the borrowing of intimate undergarments specific to the marital bed, the more accurate ruling is prohibition. This is because such garments pertain to one's private parts and the most intimate secrets of the spouses, and no one should be privy to them or spread information about them. The prohibition is further emphasized if the clothes belong to a specific woman known to the husband, as this is considered a divulging of secrets and contrary to modesty and chivalry. It is narrated in the Hadith: "Among the worst people in station before Allah on the Day of Resurrection is the man who is intimate with his wife and she is intimate with him, then he spreads her secret." This implies the prohibition of divulging what transpires between spouses regarding intimate matters.