(4) باب فِي الْخِضَابِ لِلنِّسَاءِ
Narrated Aisha, Ummul Mu'minin:
A woman made a sign from behind a curtain to indicate that she had a letter for the Messenger of Allah (ﷺ). The Prophet (ﷺ) closed his hand, saying: I do not know this is a man's or a woman's hand. She said: No, a woman. He said: If you were a woman, you would make a difference to your nails, meaning with henna.
Reference: Sunan Abi Dawud 4166
In-book reference: Book 35, Hadith 8
English translation: Book 34, Hadith 4154