Narrated Aishah, Ummul Muminin: 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.
Related hadith on this topic
Explanation & Benefits
Shaykh Umar Farooq Saeedi
Benefits and Issues:
It is recommended that at the very least, a woman’s fingernails be dyed with henna so that she remains distinct from men.
Nail polish may also be applied, but some scholars state that purification (taharah) is not achieved with it, because the polish does not allow water to reach the body; however, this is not the case with henna. Therefore, it is necessary to avoid nail polish.
According to some scholars, this narration is hasan (good).
Source: Sunan Abu Dawood – Commentary by Shaykh Umar Farooq Saeedi, Page: 4166