´It was narrated from 'Aishah that:` A woman reached out her hand (to give) a letter to the Prophet [SAW], and he withdrew his hand. She said: "O Messenger of Allah, I reached out my hand (to give you) a letter and you did not take it." He said: "I did not know whether it was the hand of a woman or a man." She said: "It is the hand of a woman." He said: "If you were a woman, you would change your nails (by dyeing them with Henna)."
Hadith Referenceسنن نسائي / كتاب الزينة من السنن / 5092
Hadith Gradingالألبانی:حسن | زبیر علی زئی:ضعيف، إسناده ضعيف، ابو داود (4166) انوار الصحيفه، صفحه نمبر 360
1؎ : From this hadith, it is emphasized that women should maintain the signs of their femininity and should not adopt anything resembling men. The wisdom behind this is, in fact, to preserve Allah’s creation as it is. Altering Allah’s creation is a forbidden (haram) act, regardless of its form. In matters related to the signs of femininity, apart from the specific distinguishing features of men and women, consideration will also be given to the customs and traditions of honor and practice in the local area and society.
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.
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