سنن أبي داود

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.