حَدَّثَنَا مُحَمَّدُ بْنُ مُحَمَّدٍ الصُّورِيُّ، حَدَّثَنَا خَالِدُ بْنُ عَبْدِ الرَّحْمَنِ، حَدَّثَنَا مُطِيعُ بْنُ مَيْمُونٍ، عَنْ صَفِيَّةَ بِنْتِ عِصْمَةَ، عَنْ عَائِشَةَ، - رضى الله عنها - قَالَتْ أَوْمَتِ امْرَأَةٌ مِنْ وَرَاءِ سِتْرٍ بِيَدِهَا كِتَابٌ إِلَى رَسُولِ اللَّهِ صلى الله عليه وسلم فَقَبَضَ النَّبِيُّ صلى الله عليه وسلم يَدَهُ فَقَالَ ‏"‏ مَا أَدْرِي أَيَدُ رَجُلٍ أَمْ يَدُ امْرَأَةٍ ‏"‏ ‏.‏ قَالَتْ بَلِ امْرَأَةٌ ‏.‏ قَالَ ‏"‏ لَوْ كُنْتِ امْرَأَةً لَغَيَّرْتِ أَظْفَارَكِ ‏"‏ ‏.‏ يَعْنِي بِالْحِنَّاءِ ‏.‏

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 (PBUH). The Prophet (PBUH) 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. Translation Not Available

Book reference: Sunan Abi Dawud Book 35 Hadith 4166
Web reference: Sunan Abi Dawud Book 34 Hadith 4154